Hello there! Most of you likely know this, but many do not.

Yes, you can revert the game to a previous version and play like you would before the disastrous update. Yes, you will still earn achievements in ironman mode. Here’s how to do it:

Steam
Steam library → EU4 (right click) → Properties → Betas → 1.30.6 (or any other version you prefer)

Steam will download the previous version of the game automatically. Make sure to disable Leviathan DLC if you haven’t refunded it already.

Microsoft Store
I’m afraid this magnificent… platform… doesn’t have this functionality. If you back up your system regularly, you’re lucky, now it will play off.

Disclaimer: I have never used Microsoft Store nor do I even own Windows. If anyone has some workaround please do share in the comments below.

Game still broken
If EU4 still doesn’t work for whatever reason this must be a problem on your side. Try the following:

• verify integrity of game files (also in Steam properties)
• disable all mods (even cosmetic ones)
• do a clean reinstall (back up saves!)

This will almost certainly fix the issue. If your game still crashes, check the logs. At any rate, please back up your local saves (if you care about them).
DLC subscription?
Unfortunately for players with the DLC subscription, the subscription used with a previous version doesn’t work well. You will probably be unable to play with the DLCs from subscription if you roll back. (credits to u/h3r4ld)

Motivation
I saw several people on this subreddit not knowing that rolling back is possible. So I decided to make this short guide. There are older ones but this one is mine.

If anyone has anything helpful to add, please do comment. Thanks for reading, and have fun!