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_keys ])

Not having installed something yet, at least now TDE's repository has also been successfully imported.

Sorry for inconvenience!