Senestoj: With Galaxy 2 the UI desing is very confusing, but Im' struggling to enter in TW3 UI garbages so I'd say this dev isn't a top gun for UI design.
Firstly the Galaxy folder option for games was the folder where is installed the game, still the game wasn't indentified, bug.
Options at top left, Add games and friends > Add game myself, get a search list, select the game... Install button lol.
I had click install to install the game already installed, sigh. But clearly it wasn't again the 2H of boredom of manual install, was quick so either it didn't install anything either installed a last patch not in downloaded files for manual install.
You never clicked Scan folder...? The Install folder is the default install folder. It will not automatically add games. The add Game feature is for games not in your GOG (or other service) account. The option to add your already installed GOG games is Scan folder(s) for GOG Games under the Add Games and Friends item in the menu, or from the big purple button on the discover page.