For some still-inexplicable reason, my externals started working again in both of these versions of Pd after building and loading a newly-created external. macOS Catalina 10.15.4.
Newly built externals are not blacklisted.
I trust you on that, but loading a newly-created external seems to have resulted in my previously-blacklisted externals also loading with no problem.
In the case of my externals, I would guess that perhaps this might be because the new and old all used the same signing certificate? But that wouldn't explain my friend’s externals which he compiled.
So perhaps there’s something else going on which I’ve missed, because no one else has confirmed this yet : \
Kevin