Briefly noted: If a 13.2 jail is no longer available on a 13.0 TrueNAS, this can be circumvented with a little trick via the shell.

iocage fetch -s http://ftp-archive.freebsd.org -d /pub/FreeBSD-Archive/old-releases/amd64/

After the download, TrueNAS will still not show the old release on the website, but a new 13.2 jail can still be created manually:

iocage create -b -n "vaultwarden" -r 13.2-RELEASE vnet="on" bpf="on" dhcp="on"

Voilá