So earlier today I tried to boot up the game and it didn't work, the background in the menu didn't load at all and pressing 'continue' means it fades briefly and then returns to the main menu.
The log says that the steamapi failed to initialize and that there's "More than 2 scenes loaded".

I was wondering if anyone else has come across this before?

The version-log has no notice in it but upon consulting the files it does seem like there was an 'update' recently, just not one that got a notice. :/

I haven't seen that particular problem, but the recent updates seem to have introduced a large number of bugs reported by many different users. I am personally having issues with some cards not stacking, time not pausing when exiting the Mansus, and the game freezing on exit. Hopefully the devs are working on it.

Are they still updating it regularly? I want to get the game on GOG, but without any patch notes posted in the stickied thread, it makes me worry the GOG version is far behind the Steam version.

The GOG version is still getting regular updates. The release notes thread isn't being updated, but the current GOG version is v2020.10.b.1.