https://www.gog.com/forum/fallout_series/cant_find_fallout_mac_save_gamed_folder

Doesn't help. Once you Show Package Contents you get the list I mentioned above with plenty of folders to chose from which would make sense to be save folders. Tried a few to no avail. As I can't launch Fallout, I can't make a fake save to figure where they actually go.

I can't tell if you're trying to be difficult or if you are really ignorant of the standard Windows filesystem...

I know that may have come across harsh, and if it's the latter, I apologize... but did you try looking inside said folders?

A Wineskin wrapper (based on the standard Wine prefix) is just a false superset of the Windows filesystem with
the requisite macOS (Contents) and Wineskin directories thrown in—i.e. "drive_c" maps to the "C:\" drive of a standard Windows installation.

Usually you'll have a drive_c folder that contains a GOG <something here> directory (or a Program Files directory which, in turn, contains said GOG ... directory) and then inside that is the game directory (something like Fallout 3 in your case). Once you're in that directory, the savegame directory can be one of a number of standard names like "SAVE" or "savegame" (or something far less obvious if the game developers were trying to be difficult).

Please find your nested game directory and then, if you still can't find the directory containing the savegame files, post a list of the associated directories in hopes that someone can help you.

...sorry for the brashness, but you literally just posted the directory listing of damn near every Wineskin game out there...