UPDATE:
I just pushed an update into the “main” branch, this now gets completely rid of the UAT scripts, i.e. no engine source build required, anymore - I replaced the “PackageUGC” call to the custom UAT script with a “BuildCookRun” one that UAT offers out-of-the-box.
This also gets rid of the above mentioned compiler error - as you don’t have anything to compile, anymore 
Only downside is, now you don’t get a ZIP, but a folder containing the mod that you can copy/move into a standalone build of the original project and/or just ZIP for uploading or w/e.