Oh, I just noticed that gpg doesn't say anything about the trust of the key if the key is expired. Compare this to the following output of gpg in case of a not-expired signing key without trusted certifications.
[GNUPG:] NEWSIG
gpg: Signature made Di 06 Jan 2026 16:35:20 CET
gpg: using EDDSA key 98FB8E8F8E5F58FA653E17A6FC9B2EF2C62AC7BE
[GNUPG:] KEY_CONSIDERED 98FB8E8F8E5F58FA653E17A6FC9B2EF2C62AC7BE 0
[GNUPG:] SIG_ID mmuLNgiB0C7AfTaVYpNjZbcVQok 2026-01-06 1767713720
[GNUPG:] GOODSIG FC9B2EF2C62AC7BE t7790-expired
gpg: Good signature from "t7790-expired" [unknown]
[GNUPG:] VALIDSIG 98FB8E8F8E5F58FA653E17A6FC9B2EF2C62AC7BE 2026-01-06 1767713720 0 4 0 22 10 00 98FB8E8F8E5F58FA653E17A6FC9B2EF2C62AC7BE
[GNUPG:] TRUST_UNDEFINED 0 pgp
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
98FB8E8F8E5F58FA653E17A6FC9B2EF2C62AC7BE
