Ubuntu 22.04 l2tp/ipsec has some problems
1. It does not start xl2tpd automatically.
2. dhcp does not set proper routing.
3. ppp0 priority is set too low.
4. It does not renew /etc/resolv.conf with NetworkManager version.

Solutions:
After the tunnel established,
1. # systemctl start xl2tpd.
2. # ip route add {destnation IPaddress}/{netmask} dev ppp0.
3. # /usr/sbin/ifmetric ppp0 700.
* You might install ifmeric first.
4. # rm /etc/resolv.conf; ln -s /run/NetworkManager/no-stub-resolv.conf /etc/resolv.conf.

If you can’t establish the tunnel, check userID and NT domain. In case you set NT domain, userID will be sent as {NT domain}\{userID}. you’d be better off leaving NT domain as blank.