I am now using GOG Galaxy.
If I would use another library manager, for example Playnite, to launch my GOG games.
Would I miss features?

For example:
Do I still get GOG achievements?
Will GOG know which games I have played and for how long?
Can GOG still give me a relevant game recomendation? (I am guessing it is partly based on purchases, library and playtime)
I am guessing my GOG profile page will not be up to date anymore with what games I have played recently.
Anything else?

Not familiar with Playnite, but other launchers are slowly incorporating features like GOG Achievements such as the Heroic Games Launcher and (possibly later down the road( Lutris.

My understanding is that GOG doesn't track anything that Galaxy can't detect, hence why offline hours/achievements don't update to your account if you decide to resume through Galaxy. So it would depend if the manager is launching through Galaxy or an offline exe.

Actually, I did have one weird moment where my Cyberpunk hours were updated, didn't happen for anything else though and didn't give me the achievements I would have gotten offline.

Whilst on the topic, what ever happened to games tracking achievements in-client. That way you never needed to be online to claim your feats.

I use Playnite, so I can answer your questions about it. A lot of this is going to depend on if you decide to integrate with GOG or if you go 100% offline. I decided to go the latter route to the extent that I manually add all games from all stores, which means no achievements or reporting anything to said store in terms of how long I have or have not played.

If you decide to integrate with GOG, I'd expect it to report to GOG and update things here. You can always test it out with one game to see how it goes.

Heroic Games Launcher has recently added support for something called comet, essentially allowing it to communicate with the Galaxy backend. On my profile you can see I have times tracked for Quake and Doom + Doom II, as well as achievements for the latter. These were gained not through Galaxy, but Heroic.

For other launchers it will probably be hit or miss.

Hope this answers your question.

Does Galaxy still launch in the background though or is it strictly tracked through Heroic? If the latter that's pretty big for PC gamers who like tracking their games since consoles have always been able to track offline.

I've only successfully tried Heroic on Linux, so no Galaxy in the background there.
To my surprise, my GOG profile started showing game activity. No achievements at the time, IIRC.

I run Heroic on Linux to do the whole GOG tracking thing. There's no Galaxy there, of course.

The way it works is that it installs the game for you (or you import it from somewhere else), if it's a Windows game then it asks you which Wine you're going to use or assume you want the default one, that's for the first time. Afterwards, just play your game. Achievements and time tracking then works.

I haven't tried if it also handles multiplayer. But yes, no Galaxy in the background.

Okay cool, thanks for the replies. That's pretty neat. I'm on Windows so I'll download it and see if it works all the same on here.

I tried Heroic once on Windows but ran into a showstopper. Looking into other reports of the same problem, it possibly had to do with my PowerShell profile setup.
Temporarily removing my non-default settings didn't fix it.
I'm fairly certain it would have been easy to debug, but Windows is obviously not the Heroic team's primary target (which is perfectly fair), so I decided to drop evaluating Heroic on there for the immediate future.

I just gave it a shot, played through an hour of Yakuza through Heroic instead of Galaxy. It gave me my hour + an achievement for completing a chapter. So it would appear as though Heroic is one way to avoid Galaxy and still track your games.

Just an update for apple, Heroic Launcher has been working flawlessly for me over here on Windows as a Galaxy alternative. Installed some games, played a few, tracking + achievements work fine.

Thank you!