This is a legacy version of GameMaker and does not receive any updates. To make sure you are on the latest version and able to get updates, search for "GameMaker" in the Steam Store. Any previous licence purchase is still valid for the new version. https://steamproxy.net/steamstore/app/1670460/GameMaker/...

After latest updates and checking out GameMaker (another app) it seems that my old version is broken. It's kust stuck on 'Building...' and doing nothing. Does this mean that GMS2 is officially unusable at this point?

Why?

Bought a lifetime licence years ago in steam. I am very disappointed that it is now missing. Is there a way for me to recover that?

In the GMS2 ToS, it explicitly states that you cannot use the engine for "pornographic" content. This kind of censorship enrages me. I plan on making and releasing an R18 game on itch and dlsite. If you were me, would you risk it and make the game on GMS2 anyway? Or play it safe and migrate to an engine that allows it?...