With mullvad, proton or iVPN, just enable lockdown mode or what proton calls the "permanent" kill switch.
That should block all unprotected traffic with no issue
Edit, I used policy plus to delay my quality updates by 30 days and my feature updates by 365 days and a couple of days ago I paused my windows updates because I saw britec09 talking about how some of the more recent updates to windows 11 will cause bluescreens sometimes. So I'm not affected.
Mullvad seems to be working, but some people have reported
that it is possible, it silently drops a connection but appears to
be connected.
I don't know how to check for that, though. Time to learn.
ipleak(dot)net is a much better test to see if your VPN is working correctly.
Swap proxies while the test is running to see if there's any leaks. that's the one thing that almost every VPN fails at protecting. Mullvad and proton are the only 2 I've ever used that don't leak.