MarsSeed [1] filed a deletion request for postgresql-11 [2]: EOL as of November 9, 2023.
The AUR package was last updated on 2022-01-30, and it was flagged out-of-date since 2022-03-10. Nothing on AUR depends specifically on this version. Safe to delete. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/postgresql-11/
