I figured out these things so far:

Trepang 2 Bladekisser dlc offline version cant be downloaded through galaxy
There are no baldurs gate 3 offfline cloud saves to download
achievemnts dont unlock in the slay the princess game

Show your issues as well

Galaxy doesn't distinguish between save game accounts. If you have another version of the game (Steam, Xbox, etc) installed alongside your GOG one, Galaxy will try to back up both. Depending on the save file size, that could break cloud saves (no more than 200 mb per game).