Tried it now, didn't work - it restored the folder, but I still get that same error. The file is there (it was there even before trying this) - but for some reason it can't find it \ load it.

Think about the kind of people who play on Steam: the easier the better.

At least it works starting the game via the executable, hm?

I wrote support about that. They are saying that there's apparently an ongoing issue with that patch and that they've contacted the game devs about that and that, if you want the newest patches, you will, for the time being, either have redownload the whole game or use Galaxy.

I for my part am using Galaxy to get me Patch 4 and then am switching back to the offline-files as Galaxy unfortunatly tries to re-download the whole game if I switch it's configuaration to another language as english. (Which the game is already installed in and are included in my offline-downloads. So patching to 4 via Galaxy and then offline-patching which has the updated loca-files it is)
(If that works. I'm currently testing it, but it might still require manualy changing the language to be applied in the language.lsx)

Yes, I run it via the executable now. But then I don't get the trophies. BTW, are game saves synced if using Galaxy?

Personally I would avoid changing the game version while you're still playing through a walkthrough.

That will very likely lead to problems.

Why? That is the easiest thing to do and make any playthrough much more safer, especially when you are using mods.

There have been situations where a patch has caused unintended consequences on certain save games made prior to the patch. I imagine they're very rare, but it does happen so if you want to avoid all risk of being one of those edge cases, pausing patches during a playthrough is one way to do that.

I install with Galaxy and allow it to patch whenever one comes available, and I've never had problems... but that's just a numbers thing. Someone, somewhere, DID have problems, thus the need to release hotfixes.

I'm talking in a very general sense, this isnt specific to BG3 at all.

You are changing the code while still using an old save and its not guaranteed that the programmer who implemented these changes did so without error, i.e. did so that your old save is actually still working properly with the new game code.

That can lead to very nearly impossibly to diagnose errors that will only apply to you alone and nobody else.

Thats why the conservative choice is to finish your game walkthrough and only then switch to a new version of the game for a new walkthrough.