Looks like this is unnecessary to set, and will only give problems when running as an unprivileged user.
2022-01-29 17:00:15 /sbin/ip link set dev tun1 up mtu 1500
RTNETLINK answers: Operation not permitted
2022-01-29 17:00:15 Linux ip link set failed: external program exited with error status: 2
2022-01-29 17:00:15 Exiting due to fatal error
bash-5.1$ ip link show tun1
1979: tun1: <NO-CARRIER,POINTOPOINT,MULTICAST,NOARP,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 500
link/none
