Why is GOG Galaxy stable version updating itself to GOG Galaxy BETA? Yesterday I got the popup and thought cool, it went final. And now I realized it still says BETA everywhere. What's going on? A typo in interface or have GOG guys really pushed BETA version to all users on a stable channel?

Nope, no typo. It's exactly what it looks like. A beta build of an interface replacing one that works properly when it's not ready for launch yet.

Here's my response:
https://www.gog.com/forum/general_beta_gog_galaxy_2.0/open_letter_to_gog_and_message_to_support

You're going to link that in every post aren't you :P Fwiw I'd say the lack of tagging support from the older version and the website is more discussed issue than any raised in that post, if we're speaking of key points. They're getting better bit by bit though, generally and GOG staff have already mentioned that UI customization (re v1.2-like lighter theme options) is a planned feature in posts last year. Not sure how the current Covid-19 situation has affected such timelines.

No. Only most of them... And if you think that, you should mention it in reply to the post. I'd appreciate more voices in there, even if they're disagreeing with me. I hadn't seen anyone else talking about how the older Galaxy client used tagging when I made the post, and it's never been a feature I've used much on any platform, so if I'm missing something big, I'd appreciate that information being in the same place as what I've said. And as I have said elsewhere (including the topic mentioned previously), I like a lot about Galaxy 2.0 and don't think they should give up on it. But it's not ready to be the only option at this stage. The older client version needs to be the primary client until 2.0 is ready and has the full complement of basic features.

you're right, it's not reasonable. they are trying to bruteforce us this thing.

All it did for me was make me download LaunchBox. I'm still on 1.2 for Galaxy, but I know eventually they'll block connections from older versions. Took a while for me to grab all the metadata for my GOG games and I still need to make some corrections for a game here and there, but I do like the customizations, sorting features, and ability to add games that run under emulators.

I just caught the "Beta" in the version before clicking "Update" like I normally would, but it was a really close one. I clicked on "Update later", but what does that mean - will it somehow force the update, currently? As in, "Update later (on next restart)", or is it an actual "No, don't update until I click on Update"?

I really don't want to be on Beta versions for any of my most commonly used applications, ever.

It auto-updates next time the client restarts but if you look through a few topics here, there are instructions in a handful of them about how to prevent it updating, or revert (by uninstalling 2.0 and reinstalling the latest 1.2 version) and block updates.

Cool. So it already downloaded the files, as I had suspected.

For anyone else searching, here's what I did. No idea if that's enough, or too much, but I made backups so, I'd rather use the sledgehammer and repair a bit afterwards than having to spend multiple hours reinstalling everything from scratch with all my custom game install paths and modded games, which would be broken by the updater when importing the folder.