Detect DNS leak and warn ProtonVPN users
An encrypted DNS (Called DoH - DNS over https) is said by you (in the later linked article) to "prevents our software from being able to see the DNS queries. This makes it very hard to block or reroute them."
causing DNS leak, which can be considered a serious privacy compromise IMO.
https://www.dnsleaktest.com
https://ipleak.net
It seems to be too severe not to warn user about it in case it is doable from the side of your application. I guess your app tries to read the DNS request and if is encrypted, it fails and can do some action, like displaying a warning inside a main ProtonVPN page, linking user to a tutorial on how to fix it ( https://protonvpn.com/support/dns-leaks-privacy/#dns-over-https or similar ).