I tried moving to the live staging tree to see if some other things are fixed, but it makes things worse. (Lightmass requires SSE “for now” which means no arm64.)
I’m switching back to the 5.1 release tree with the patch. I tried the file again. The patcher launches, but is unable to find my engine installation. (As I’m compiling from GitHub, it’s not in a standard location.) I still have to apply the patch manually.
@fawazart if you’re still having trouble, the files in UnrealQFEInstaller.app/Content/Engine need to be copied to the same location in your code tree’s “Engine” folder, replacing the files that are there.