If computers are in same network, even with different ip addresses, they still can see all broadcast and multicast traffic. This means for example dhcp.

If you fully trust your computers, and are sure that no external party can access any of them, you should be fine. But if anyone can gain access to any of your computers, it is trivial to gain access and sniff traffic in all networks.

If you need best security, multiple switches and multiple nics are unfortunately only really secure solution.

Luks FDE, and install dropbear-initramfs, configure ssh authorized_keys and rebuild initramfs. Then you can access initramfs via ssh to type luks password.

Have you ever upgraded the Ubuntu laptop? Cause that’s my main gripe with Ubuntu. Server upgrades work, desktop upgrades never did for me.

I wonder about this. I have been running Ubuntu on one of my laptops for years, and updated it several times withouth hitch. All the way from around 18.10 to 22.04 (non-lts, so I upgraded to every release) until the laptop was replaced.

Usually the breakage happens if one has tons of shitty third-party repos and thus will get package conflicts when upgrading. And those are solved by removing/replacing all software installed from those repos and then after upgrade reinstalling them again if needed.

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.

Ventoy? https://www.ventoy.net/en/index.html