The ethical route, ie “white hat”, is to contact the owners about the exploit with a fixed period disclosure. Ie, “fix this in 30-90 days, or we will publish our method”.

I’m not sure that is the ethical route when you’re talking about disrupting the operations of a Nazi-led government.

Anyone who leaves a message in full view to announce they’ve accessed the system isn’t the real danger. If whoever this is could get in, so can the real experts from China, Russia, North Korea, etc. There’s no way Musk’s DOGE people, in their destructive haste, have taken any care over security. It’s even likely his team of punchable kids put in their own backdoors, thinking they were being clever. If and when foreign adversaries find their way in through those, they’re not putting up an announcement.

Not all of these mini PCs have a wifi card in them even if they have the antennas for it. You might start by opening it to check whether the wifi antennas are connected, or whether you need to add a WiFi card.

I think OPNsense would do what you’re looking for. I use it on a mini PC as my router, and it’s great, but I have not used it for WiFi (I run a separate access point). The limitation is WiFi hardware support. You will need to make sure your mini PC’s WiFi card has a driver in FreeBSD. Intel hardware is often a better bet than Realtek etc.

https://docs.opnsense.org/manual/how-tos/interface_wireless_internal.html