It appears the Galaxy overlay does not work.

I found a supposed fix on the forums but couldn't get it to actually work (forum won't allow me to post a link though :( ).

Has anyone here had any success getting the Galaxy overlay to work with Succubus?

This one?

https://www.gog.com/forum/general/galaxy_overlay_fixes_for_games_that_are_officially_supported/post1

Did you follow the instructions how to install the overlay fix?

I did, twice, to make sure I didn't miss any steps, and it still does not show up for me. Tried checking if there might be locale related issues with regards to the info file but all that seems to just be standard, so not entirely sure what the issue is.

Steam overlay works fine though, ironically ...

That's strange. The most important thing of the instruction is that the game shows as not installed when you restart Galaxy.
Also, did you check if the overlay is activated in the Succubus Galaxy settings?

Here are two screenshots of the fixed overlay.

Yes, the overlay works fine after using the fix Hustlefan posted in his thread. As he said it is very important to make sure that the game does not show as installed when starting Galaxy (by moving the folder or the ini file itself elsewhere). It is also important to copy the file(s) back while Galaxy is still running. If you import the game from within Galaxy and if you made sure that you did not deactivate the overlay in the settings it should work.

On a sidenote: the devs are aware of the problem and told me that they might fix it soon if it is not too hard to fix.