grep mtu /etc/config/wireguard will show whatever’s been applied to the saved profile’s MTU. You’d still need to disconnect & reconnect WG via the GL GUI though. See below for resources to gain access via SSH (typically root@192.168.8.1).
logread is also available to read the full system logs. logread -e firewall is an example of how to ‘filter’ for firewall related entries. wg is for WireGuard. I don’t know about OVPN as I don’t use it. You may be asked to post your ip route given the OVPN + VPN Policies difficulties.
Don’t forget to include your device model & firmware version (GL GUI → System → Upgrade → Online Upgrade).