In my experience, I first booted with recovery mode and typed:
nvram boot-args=“no32exec=0”
and, downloaded zip file from @pkman99. Next, open zip file, moved to Applications folder, and typed command in terminal (it's quite different from original post):
sudo xattr -rd com.apple.quarantine /Applications/PKHeX.app
Finally, I opened it with secondary clicking and click "open" of PKHeX application in Applications folder.