Just to clarify - I found several patches missing and personally don't like big gaps.
So this does not mean that GOG waited 2 years for a patch but that the volunteers
had not played catch-up with the latest changes.

Thus the current 4.1B version on Linux and 4.1A version on Windows and macOS arrived
at GOG on 15. April 2021 in Offline Installer (I don't use GOG client - and even wouldn't
 if it would be available for GNU/Linux - which isn't - thus I can't give that date).
And this patch arrived on Steam on 1st March 2021 - with the above changelog.

So I hope this explains what happens ... and I hope most will prefer full changelogs
despite being a little confusing - but each changelog has it's date - it just differs
substantially with the date of the uploading here.

And thus people wondering to purchase it can see that the GOG version is currently up-to-date -
and macOS users can see that the patch for macOS Big Sur has arrived.

Cool. Thanks.

I'm currently playing 4.1. Linux version. Hope updating to 4.1B won't cause issues with saves.

So the only thing new in this versin is the Arby's promotinal DLC?

Yes, this DLC seems to be the only new thing mentioned.
4.1 (36252) => 4.1b [Arby's] (46298) seems like additional 10000 patches ...
so I am not sure and I have not tested it - just installed and started it without problem.