Update:
gpg --verify Downloads/electrum-4.1.5.dmg.ThomasV.asc Downloads/electrum-4.1.5.dmg
gpg: Signature made Mon Jul 19 11:22:27 2021 PDT
gpg: using RSA key 6694D8DE7BE8EE5631BED9502BD5824B7F9470E6
gpg: Good signature from "Thomas Voegtlin (
https://electrum.org) <
thomasv@electrum.org>" [unknown]
gpg: aka "ThomasV <
thomasv1@gmx.de>" [unknown]
gpg: aka "Thomas Voegtlin <
thomasv1@gmx.de>" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
The .asc (PGP signature) file for that command was the one downloaded from the Electrum site -- the one that I cannot import into GPG. But if I try to use the one @NeuroticFish kindly provided, which I can import, I get:
gpg --verify Downloads/ThomasV.asc Downloads/electrum-4.1.5.dmg
gpg: verify signatures failed: Unexpected error