Yeah there is no way to fix that. If someone stole or found your mifi, even if they don’t have a pin for the simcard, they can just connect to the lan port and use it, so the pin is useless.

If you loose or the device is stolen, just quickly call the operator to block the sim and get a new one.

It is possible to disable the lan ports using Luci, its the “Advanced Settings” in the top right of the GL-iNet UI.
There is no way to add a password to the LAN; but you can have it so only specific MAC addresses can get an IP. It will still not help cos people can set a static IP…

Either way the person can reset the Mifi and connect using the default password.
When you reset the Mifi, the modem is not reset, it still holds the PIN (if it worked…)