Blizzard have detailed everything about the sixth ladder season of D2:R, with the new addition coming on the 22nd! We have regional launch times, the different modes, and an explanation on what happens to shared stash items for seasonal character after it ends, so let's take a look.
Season 6 (Source)
The lords of Hell await your return, traveler.
Countless demons have met their timely demise at the end of your weapon, yet their onslaught doesn’t relent. Sanctuary needs its savior! Return on February 22 to wreak havoc among the Burning Hells’ ranks in Ladder Season 6!
Ladder Season 6
Our previous Ladder Seasons for Diablo II: Resurrected have showed just how adept adventurers were at saving Sanctuary, racing to be the first to cement their names on the Leaderboard, while striking fear into the tormented hearts of their demonic adversaries in the process.
Ladder Season 6 will usher in a fresh opportunity for brave adventurers to race to Level 99 and amass powerful loot along the way.
Ladder Season 6 Launch Timing:
North America February 22, 05:00 p.m. PST
Europe February 22, 02:00 p.m. CET
Asia February 23, 10:00 a.m. KST
As with previous seasons, Ladder Season 6 will feature different modes:
Version Description Pre-Expansion Ladder The standard version of Ladder play that encompasses only the original four acts. Pre-Expansion Hardcore Ladder The hardcore (only one life) version of Ladder play that encompasses only the original four acts. Ladder The standard version of Ladder play that encompasses five acts, as it includes the “Lord of Destruction” expansion content. Hardcore Ladder The hardcore (only one life) version of Ladder play that encompasses five acts, as it includes the “Lord of Destruction” expansion content. For those new to Ladder Seasons, you might be wondering what happens to your Shared Stash loot once the current season ends.

Once Ladder Season 5 ends, all Ladder characters will be transferred to their respective non-ladder group. All items in that character group's Shared Stash go into a new Withdraw Only set of Shared Stash tabs, denoted by a check marked Past box. Any items from Ladder Season 4 stored in the Withdraw Only tabs will be lost at this time. You will have all of Ladder Season 6 to withdraw any items you would like to keep from Season 5. When Ladder Season 6 ends, this withdraw only set of Stash Tabs will be overridden with any items in the Ladder Season 6 Shared Stash. Be sure to get any items out before then or they will be forever lost!
May your Ladder race be filled with fiends to eviscerate and bountiful loot.
-The Diablo II: Resurrected Team

From December 12 through January 3, the 22 Nights of Terror holiday event will be available in Diablo II: Resurrected.
(Source)
The air stirs with whimsey, perhaps even magic, adventurer.
However subtle, a joyous invocation permeates Sanctuary, casting a ray of holiday celebration upon its inhabitants. . . or is this demonic trickery? This magic from beyond is not cause for a ceasefire in the unremitting conflict between demon and mortal, but its nuances can still be felt, disturbances are surely lurking about. Seeing this holiday miracle through to the end relies on you—sleigh your way through 22 Nights of Terror during the Diablo II: Resurrected holiday event.
Experience Daily Demonic Trickery
The magic constantly shifts day by day but remains pervasive in nature—even Sanctuary’s most esteemed scribes are unable to predict what abnormalities the future might hold.
From December 12, 11:00 a.m.–January 3, 11:00 a.m. PST the fabric of Sanctuary will be altered every 24 hours, revealing a new gameplay modifier via the in-game Message of the Day that will last for the next 24 hours. The 22 Nights of Terror holiday event can be enjoyed in all online game modes except for Classic Diablo II.
Powerful loot, a dash of terror, and a new surprise to experience each day awaits you in Sanctuary this holiday season. Go forth in glory!
Happy holidays!
-The Diablo II: Resurrected Team

A new season of D2:R has started! You can see the official post below and you can also check out all our guides for it here or head to one of the guides below.
Diablo 2 Recommended Starter Builds Hammerdin Blizzard Sorceress Trapsin Summoner Necromancer Lightning Fury Javazon Wind Druid Meteorb Sorceress Smiter Paladin Bone Necromancer
  Farming Guides Andariel Run Guide Baal Run Guide Chaos Run Guide (Diablo) Mephisto Run Guide Cow Level Run Guide Lower Kurast Run Guide
  Other Guides PvM Rankings Runes   Season 5 (Source)
We knew you would return traveler…and so did Hell’s minions.
Countless demons have met their timely demise at the end of your weapon, yet their onslaught doesn’t relent. Sanctuary needs its savior! Return on September 28 to wreak havoc among the Burning Hells’ ranks in Ladder Season 5! Read further to glean pertinent information about the Season.
Ladder Season 5

Our previous Ladder Seasons for Diablo II: Resurrected have showed just how adept adventurers were at saving Sanctuary, racing to be the first to cement their names on the Leaderboard, while striking fear into the tormented hearts of their demonic adversaries in the process.
Ladder Season 5 will begin on September 28, ushering in a new opportunity for brave adventurers to race to Level 99 and amass powerful loot along the way. We cannot wait to see which determined souls carve their name into the Leaderboard this time.
Ladder Season 5 Launch Timing:
North America September 28, 2:00 p.m. PDT
Europe September 28, 11:00 p.m. CEST
Asia September 29, 6:00 a.m. KST
As with previous seasons, Ladder Season 5 will feature different modes:
Version Description Pre-Expansion Ladder The standard version of Ladder play that encompasses only the original four acts. Pre-Expansion Hardcore Ladder The hardcore (only one life) version of Ladder play that encompasses only the original four acts. Ladder The standard version of Ladder play that encompasses five acts, as it includes the “Lord of Destruction” expansion content. Hardcore Ladder The hardcore (only one life) version of Ladder play that encompasses five acts, as it includes the “Lord of Destruction” expansion content. For those new to Ladder Seasons, you might be wondering what happens to your Shared Stash loot once the current season ends.

Once Ladder Season 4 ends, all Ladder characters will be transferred to their respective non-ladder group. All items in that character group's Shared Stash go into a new Withdraw Only set of Shared Stash tabs, denoted by a check marked Past box. Any items from Ladder Season 3 stored in the Withdraw Only tabs will be lost at this time. You will have all of Ladder Season 5 to withdraw any items you would like to keep from Season 4. When Ladder Season 5 ends, this withdraw only set of Stash Tabs will be overridden with any items in the Ladder Season 5 Shared Stash. Be sure to get any items out before then or they will be forever lost!
May your Ladder race be filled with fiends to eviscerate and bountiful loot.
-The Diablo II: Resurrected Team

It's time for some Diablo 2 news as Blizzard just announced Ladder Season 5 coming on September 28!
(Source)
We knew you would return traveler…and so did Hell’s minions.
Countless demons have met their timely demise at the end of your weapon, yet their onslaught doesn’t relent. Sanctuary needs its savior! Return on September 28 to wreak havoc among the Burning Hells’ ranks in Ladder Season 5! Read further to glean pertinent information about the Season.
Ladder Season 5

Our previous Ladder Seasons for Diablo II: Resurrected have showed just how adept adventurers were at saving Sanctuary, racing to be the first to cement their names on the Leaderboard, while striking fear into the tormented hearts of their demonic adversaries in the process.
Ladder Season 5 will begin on September 28, ushering in a new opportunity for brave adventurers to race to Level 99 and amass powerful loot along the way. We cannot wait to see which determined souls carve their name into the Leaderboard this time.
Ladder Season 5 Launch Timing:
North America September 28, 2:00 p.m. PDT
Europe September 28, 11:00 p.m. CEST
Asia September 29, 6:00 a.m. KST
As with previous seasons, Ladder Season 5 will feature different modes:
Version Description Pre-Expansion Ladder The standard version of Ladder play that encompasses only the original four acts. Pre-Expansion Hardcore Ladder The hardcore (only one life) version of Ladder play that encompasses only the original four acts. Ladder The standard version of Ladder play that encompasses five acts, as it includes the “Lord of Destruction” expansion content. Hardcore Ladder The hardcore (only one life) version of Ladder play that encompasses five acts, as it includes the “Lord of Destruction” expansion content. For those new to Ladder Seasons, you might be wondering what happens to your Shared Stash loot once the current season ends.

Once Ladder Season 4 ends, all Ladder characters will be transferred to their respective non-ladder group. All items in that character group's Shared Stash go into a new Withdraw Only set of Shared Stash tabs, denoted by a check marked Past box. Any items from Ladder Season 3 stored in the Withdraw Only tabs will be lost at this time. You will have all of Ladder Season 5 to withdraw any items you would like to keep from Season 4. When Ladder Season 5 ends, this withdraw only set of Stash Tabs will be overridden with any items in the Ladder Season 5 Shared Stash. Be sure to get any items out before then or they will be forever lost!
May your Ladder race be filled with fiends to eviscerate and bountiful loot.
-The Diablo II: Resurrected Team

The Classic Diablo 2 ladders will reset on June 22 with a 4-hour downtime starting at 11 am PT.
(Source)
Hello -
We will be resetting the Classic Diablo II ladders on June 22, 2023 at 3pm Pacific Time / 6pm Eastern Time.
There will be a 4 hour downtime starting at 11am Pacific Time / 2pm Eastern Time for this reset.
Please note this is for the Classic/Legacy client and not for the Resurrected client of Diablo II.