Is there a way to keep updating your offline gog collection without having to manually visit and download? I just noted some games have been updated over the years but I can't afford the time to keep updated offline versions.

Does GOG galaxy have a feature for this?

Not an official feature of the site, but there's this community-made Python script called gogrepo that does exactly what you want:
https://www.gog.com/forum/general/gogrepopy_python_script_for_regularly_backing_up_your_purchased_gog_collection_for_full_offline_e/page1

You can’t afford to once in a while check? I mean I have quite a lot and just check once a month or two months. Maybe takes half an hour. It’s really not any effort and it’s mainly if you buy indev or new games which have lots of updates.
But then, if you can’t be bothered, just go rent them off steam...

I use lgogdownloader (thread here) but if you're not on Linux then gogrepo.py (thread here) does the same thing. Don't know or care about Galaxy. Surely you jest.

346 games on gog. I just bought the last dlc for battletech so I refreshed. Also updated Warband. But 346 games...

Years ago, back when gogrepo wasn't a thing yet and I had mere 500-600 games on GOG, I tried to keep my GOG installer collection up to date, but it felt quite hard and time consuming.

I constantly lost track of what was updated e.g. because the update flag for a game was cleared if I merely went to check its changelog to see what was updated. Sometimes the update may be for the OS version I am not interested in etc.

It was even harder to keep track of what existing files had become obsolete and could be safely deleted, and later I've also found out there are "silent updates" with no update flag.

Pretty much all those problems went away with gogrepo, thankfully. I have now like 1800 GOG games, and keeping them up to date is quite easy with gogrepo. Gogrepo has become a reason for me to prefer buying from GOG, even if the same game is available DRM-free elsewhere too. I don't run gogrepo constantly, more like once a month or two months, sometimes even less frequently.

GOG could make an official version of gogrepo, maybe adding p2p technology as well so that mass downloaders like myself wouldn't hit GOG's content delivery servers that bad, and it might even give downloaders faster download speeds. Humble Store at least used to offer an option to download HB game installers with a torrent client, so it can be certainly done.

I personally would be fine with that, even if it means I couldn't use it in Linux (unless Galaxy works fine in Wine).

Maybe it could even be developed so that Galaxy would do the "update" part of gogrepo (ie. checking what has been updated in your library), and then it would just optionally pass the download links to whatever bittorrent client you have.

Anyway, I am not expecting GOG to do it as it is most probably lower priority to them. As long as they don't try to actively block the use of gogrepo or similar third-party tools, I am fine.

Do not forget to follow the thread:
https://www.gog.com/forum/general/the_what_did_just_update_thread

Because quite some GOG games never get update flags, while in fact they did get updates.

Some years ago I used the then already outdated gog downloader to get everything from my library.

But I need to update that.

Big assumption. Some of us like Galaxy for the convenience. Not everyone uses it for online tracking or anything else, though I like that too. I also keep all my games updated with the offline installers. About once a month I have 100 GB worth of update downloads to do, including new games I bought. All updates aren't marked because GOG sucks at that. And all changelogs aren't instantly updated, cause they suck at that too. That's why GOGRepo is so nice, it can look at all game files compared to previous files and download the changes rather than pray GOG properly marks a game as updated.