After 40 something minutes of tinkering. I was able to get a custom script written (With the help of AI) to get the advanced kill-switch working with Proton and NextDNS on a custom timer.

After a little bit of tinkering around with ai. I was able (From the appearance of it) with every reboot, and just manually requiring opening up NextDNS, and the auto start enabled (Just enable Auto start, and then manually click or double click GUI ProtonVPN). I can also confirm that NextDNS works with ProtonVPN and advanced Killswitch enabled, as well.

Not trolling or crap posting. I had some really bad experiences getting the kill switch feature to work with every iteration of Linux, I used. Especially along side NextDNS.