UPDATE on this one:
(1) Failure of the Trinity repo integration
[ ... ]
# joe /etc/pacman.conf ... [trinity] Server = https://mirror.ppa.trinitydesktop.org/trinity/archlinux ...
Updating the system then fails:
# pacman -Syu error: trinity: signature from "Trinity Desktop Environment Archive Signing Key" is unknown trust error: failed to synchronize all databases (invalid or corrupted database (PGP signature))
RTFM!! o_O – My fault: I simply didn't finish the process of properly importing the key (cf. [ https://wiki.archlinux.org/title/Pacman/Package_signing#Adding_unofficial_ke... ])
Not having installed something yet, at least now TDE's repository has also been successfully imported.
Sorry for inconvenience!