Next DNS

E24 then use nextDNS.

I will tell you you have to research domains, because you won't know what you're looking at. Its a game of wtf is that and what does it do when you see random domain request popping up.

The best way to check is close all apps, run DNS logs, open one app at a time, analyze the logs and figure out what is and isn't necessary for the app to function. Block everything else. You'll do this by searching the domain online and seeing if theyre analytics or whatever unnecessary garbletigoop.

E24 A VPN already prevents your ISP from tracking your online activities. If you can splurge on a paid plan many will often block ads system-wide too.

If you want to both hide your online activities and block ads without upgrading to a paid ProtonVPN plan, you can use both the free VPN and NextDNS, but you will be standing out from other users and they won't work well together (your particular issue is related to something else but you nevertheless are having troubles right out of the gate).

E24 It says " network has no access, private DNS server could not he accessed"

I did observe something like this, both on GrapheneOS and on stock, with other Private DNS (AdGuard's public DoT, Control-D...). All works well, and at some point I would receive a system notification about having lost Internet connectivity, and the Private DNS provider could not be reached. It would not happen outside of my home/when I was only using mobile data. I did not use a VPN.

I found out that on my home router, I had set up all DNS queries to be redirected to another provider (can't remember if it was AdGuard or else). Once I removed that from my setup, I ceased having connectivity issues. Maybe there is some kind of race condition when hopping with 2 different providers? I don't know...