Dumdum you're no dumdum, that was an excellent temporary solution, thank you! And I think I almost prefer this lightweight wireguard app. Using this with split tunneling for mysudo is working correctly so far.
I wouldn't call the issue solved yet since something is definitely wrong with the protonVPN app split tunneling after the latest update. If we can't solve the problem here, is there a way to submit this bug to a dev so they can take a look?
Thanks again!