Questions about setting the DNS manually VS NextDNS app

Hello NextDNS community!

I noticed that the NextDNS app is sometimes a hit or miss. Even when the app is running in the background my PC is using sometimes my ISP DNS. That's why I manually change the DNS settings to NextDNS on my PC. And I have some questions.
The NextDNS app is overriding the windows settings?
For the IPV6 should I set DNS over HTTPS also to ''On (manual template)'' and set it to the NextDNS DNS over HTTPS?