While most of my GOG games will run without being "installed" in Windows (all of my games are on an external drive), my favorite launcher, Playnite, requires installation in order for the GOG library integration to work. According to the people at Playnite, there's something different about GOG Galaxy that makes different from other launchers such as Seam, Itch and Epic, so if the games are not installed, the library integration will not work.

So, back to the question, is there some sort of batch script that I can run to point to all of the setups files in a directory and install of my GOG games?

Cheers

The "something different" for installing vs using games already installed (eg, reusing games pre-installed to a 2nd HDD after reinstalling Windows on primary SSD) is probably the Galaxy Metadata registry entries the installers write to:-
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\GOG.com

You may well need to reinstall them to get that data now, but for future use it's certainly possible to export the above key (once everything is installed "normally") to a .reg file and then reimport it later on. As for batch scripts, I'm not entirely sure that the GOG installers (that use InnoSetup) can do that.

Oh, sorry, I have no idea.

Bots usually don't, they just post random replies to threads they have no idea about the subject matter...

That's strange. It's normally the "gameID", "buildId", "productID", etc, entries that are Galaxy specific. I've never used either Playnite or Galaxy though so it may well use other registry keys.

After further testing, it seems to be a crap shoot, works sometime, doesn't work other times.