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Mine has OpenWRT. It works, but doesn't cooperate with the ISP supplied Cisco router so I sadly couldn't give my boys a clean WiFi connection from their room that's on the other side of the apartment.

If you have some hardware around, look at OPNSense.
https://opnsense.org/

Thanks, I'll check whether I could use something like this. I do have some old computers stored that I may put into use.