I cannot figure out how Galaxy handles the save game folders but my save games used to be on my C drive inside OneDrive\Documents\My Games but after moving my onedrive to a different drive, I am not able to point the games to the new location. Does anyway know how that works?

I'm looking specifically for Deus Ex Mankind Divided...

Erik.

Type "run" on Win start menu and paste this,
%USERPROFILE%\Documents\My Games\Deus Ex Mankind Divided\Saves\

I have the save issue (the game won't create a new save file), it is installed under 2ed drive (E:\Gaming\Deus Ex Mankind Divided), and gog galaxy is installed on 1st drive (C:\Program Files (x86)\GOG Galaxy). How can I solve the issues?

Galaxy doesn't deal with save game locations - it's up to each game individually.
And this thread belongs in the Galaxy subforum.

PCGamingWiki usually has a list of the location used by a game to save profiles&shit for the user.

I don't know if this will be of any help but I just installed this game recently and the save folder was in My Documents not in My Games