XenonS: And then very important:
If you update to 2.11 your savegames will be wiped (not sure if I did hit the wrong option when uninstalling, so this may be the cause). You must backup them before if you want to go on with them !
Also since Beyond, the offline downloaders will give you NO online connectivity for the game, for that you need to play through GoG Galaxy.
I just uninstalled the game via GOG Galaxy, then uninstalled GOG Galaxy, then installed the game from the 2.11 offline backup installers ..
.. And all is fine, no missing save games the game continued without issue.
As for "No online connectivity" message on the discoveries screen, this has always been the case for GOG Offline Backup Installers since day 1, connectivity and anything multiplayer requires the GOG Galaxy client.
I have a bug report submitted to HelloGames Zendesk asking them if they will remove this redundant message for none galaxy users.
The game already can detect that it has no connectivity, because you will also notice you dont get the Network options listed in the games settings menu, they are hidden when you have just the Offline Backup without Galaxy.
So why do we see this "No online connectivity" message on the Discoveries screen, its no use and the game could hide it just as well as it can the Network Options menu .. We still get units for "pretending" to do the uploads, so whether connectivity is online / offline makes no difference to the player.
Edit : I wonder if you had saves you are trying to continue which previously have seen some multiplayer / online connectivity .. But are now not valid due to not having Galaxy installed and cant be used by the game. Even if I temporarily install the game via Galaxy to beta test the experimental versions of the game occasionally, I do not allow any online settings, I disable them, so my saves are always good no matter whether I have Galaxy or not (though its rare I will continue from beta testing saves, usually I re-install my backed up saves when reverting to none-experimental to ensure nothing experimental messes up my ongoing game - On this occasion I tried the saves made by experimental before replacing them with my backups, and had no issue with either when trying just to continue with 2.11).