Diablo 2's last patch to make changes to class balance was 1.13c, released on March 23rd, 2010. Now Diablo 2: Resurrected is getting new tweaks to class balance, as explained in a Blizzard blog post. Ladder rank play is also on the way in early 2022.
The post says that the changes to classes are being made "to expand character build diversity, and retain class fantasy and specialty." Without drilling down into the specific changes to come, they then talk about the philosophy behind each class revision.
For example, they intend to buff the strength of the Amazon's underused melee skills such as Impale and Feud. For the Assassin class, they want Martial Arts builds to be more viable at high difficulties, and so "are re-evaluating how to improve generating and spending Combo Points." For the Necromancer, they're planning to "improve specific Summons", making lesser-used Golems more effective.
The pattern is the same for each description: broadly they think the class is good as-is, but they "see exciting opportunities" to tweak a few variables and make some playstyles easier to do or more useful.
Ladder rank modes, meanwhile, will match those available in the original game: standard, hardcore, standard expansion and hardcore expansion. Advancing through ladder rankes will unlock all-new "Rune Words" which can only be used in Ladder play. When a Ladder season ends, your character will move to a "non-Ladder" version of the game, and you'll need to create a new character to play the new ladder. Ladder ladder ladder, lads lads lads. They currently think each season will last around four months.
You can read the whole post for information on changes to other classes, as well as to Mercenaries, items and more.