$ zfs create -p zroot/jails/releases/13.1-RELEASE
$ fetch https://ftp.freebsd.org/pub/FreeBSD/releases/amd64/amd64/13.1-RELEASE/base.txz -o /tmp/base.txz
$ fetch https://ftp.freebsd.org/pub/FreeBSD/releases/amd64/amd64/13.1-RELEASE/lib32.txz -o /tmp/lib32.txz
$ tar -xf /tmp/base.txz -C /jails/releases/13.1-RELEASE
$ tar -xf /tmp/lib32.txz -C /jails/releases/13.1-RELEASE
$ env UNAME_r=13.1-RELEASE freebsd-update -b /jails/releases/13.1-RELEASE fetch install
$ env UNAME_r=13.1-RELEASE freebsd-update -b /jails/releases/13.1-RELEASE IDS
$ zfs snapshot zroot/jails/releases/13.1-RELEASE@p0
$ zfs clone zroot/jails/releases/13.1-RELEASE@p0 zroot/jails/templates/base-13.1-RELEASE
$ zfs clone zroot/jails/releases/13.1-RELEASE@p0 zroot/jails/templates/skeleton-13.1-RELEASE
From 13.0-RELEASE to 13.1-RELEASE
rm -rf /jails/templates/skeleton-13.1-RELEASE/bin/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/boot/*;
chflags -R noschg /jails/templates/skeleton-13.1-RELEASE/lib/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/lib/*;
chflags -R noschg /jails/templates/skeleton-13.1-RELEASE/libexec/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/libexec/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/rescue/*;
chflags -R noschg /jails/templates/skeleton-13.1-RELEASE/sbin/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/sbin/*;
chflags -R noschg /jails/templates/skeleton-13.1-RELEASE/usr/bin/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/usr/bin/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/usr/include/*;
chflags -R noschg /jails/templates/skeleton-13.1-RELEASE/usr/lib/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/usr/lib/*;
chflags -R noschg /jails/templates/skeleton-13.1-RELEASE/usr/libexec/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/usr/libexec/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/usr/sbin/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/usr/share/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/usr/libdata/*;
chflags -R noschg /jails/templates/skeleton-13.1-RELEASE/usr/lib32/*;
rm -rf /jails/templates/skeleton-13.1-RELEASE/usr/lib32/*;
$ zfs snapshot zroot/jails/templates/skeleton-13.1-RELEASE@skeleton
$ zfs clone zroot/jails/templates/skeleton-13.1-RELEASE@skeleton zroot/jails/jails/testboxen_13.1