Rimworld

Depends how far back you go. Obvs, not all mods are keeping up as the game updates, but if anything, I find that the modding community has only every grown and gotten better with time.

I think that mod versioning was introduced in 1.1 (so about when Royalty released), which made it a lot easier to keep track of what works and what doesn't, so you might have issues with mods from before then, but honestly there'll almost certainly be a replacement if something was popular and was discontinued.

There are still an ungodly amount of mods for literally anything. All of the Vanilla Expanded mods are very high quality, plenty of older mods are still either updated or have been remade, and there are plenty that integrate with the new systems added by the DLC.

Honestly, if anything mods have just gotten better from them. The vast majority of mods you'd recognise from then are either still updated or have been forked/continued or superseded.

Mods are still going strong. Many of the big devs are still kicking out new and innovative mods to transform the gameplay.

There's some that aren't updated but if they were big they were probably replaced. There's so many of them. You'll be fine installing mods, just check the description and comments on the Steam workshop page.

sos2 is on an experimental git branch. It has a few positive changes but also some negative ones. For example it simplifies the way shields and heat works. On the other hand, ship salvaging has to be done by hand and is no longer automatic which REALLY makes the game drag on and on and makes ship combat really really shitty since it takes 1 year just to harvest a ship and profit off of a fight. Also the ship combat has been rebalanced to make it easier for the enemy in ways I don't agree with. I was able to hack most of the stuff I don't like with dnspy but I haven't figured out how to reverse the salvaging yet.

Android Tiers, another important mod doesn't work as well anymore but there's a VE android mod now. I still use Android Tiers just because I don't like mechtech crap and I like the feel of using "alternate" technology. Beyond that, any old 1.3 or 1.2 mod that doesn't work anymore has been replaced with something better anyway.

There were a handful of big mods that were abandoned by their devs and weren't updated when the DLCs came out. Many of those broke even though they only made some simple change. If you notice any mods are broken as you're getting set up again, go to the workshop page for the mod and check the comments for links to other mods that fill the same purpose. Often a good Samaritan will have forked and restored the mod to working order.

There's SO MANY MODS. Many of the old ones are still kicking, some were adopted, some by the original developers. If you plan on doing a heavily moded gameplay, I'd suggest looking into optimization guides tho, some mods that used to be a must have back in the day now have better, performance-friendly options.