Do you mean upgrade or reinstall?
I have done release upgrades in multiple occasions all the way from 16.04 -> 18.04 -> 20.04 -> 22.04 -> 24.04. Usually they work fine, but of course back up your stuff first. When doing it with release-upgrade all your stuff is of course kept just like before.
Basically just:
sudo apt update
sudo apt dist-upgrade
sudo reboot
sudo do-release-upgrade
This will upgrade to 22.04. After upgrade just repeat process to upgrade to 24.04
The C64 Mini and C64 Maxi are readily available today and affordably priced, making spare parts easily accessible.
If those work well enough for them, I cannot see any benefit of upgrading.
Can you access your wan ip when you are somewhere else than on your own lan?
If not, then this is probably just that your router does firewalling and nat is such order that you can access admin interface from local network via wan address.
If yes, then router has some serious misconfiguration.
They are still on the ship, and cannot get to land because of the lack of visas.