What worked somewhat okay for me was rooting the phone to edit the hosts file, but this was really cumbersome and left many loopholes that I only found afterwards. Then the root access suddenly disappeared, so I can no longer close these loopholes. I didn't really understand the rooting process (on Samsung Android), it was just patched together from various tutorials, so I can't explain why this happened or how to fix it.
Blocking directly in the router also worked a bit better than other methods, but can be bypassed by switching to mobile internet, and my current router doesn't support it anyway.
If anyone has any suggestions for me, it would be super helpful. So far my last resort would be to get a different phone for which it is easier to acquire root access, but I hope there is a better way.
Parental controls generally and there is a range of accountability software too: https://en.wikipedia.org/wiki/Accountability_software
Regarding NextDNS, can it be setup in a way that is difficult to disable? Or could I just disable the user application on my phone and use my unfiltered mobile internet? Same for accountability softwares, are there any that go below the user application level to stop me from simply disabling them?
Google parental controls seem cumbersome, as apparently I can only block domains in Chrome and will thus also need to block other browsers. But I will play around with it and see if I can make it work for me.
You may need a friend that can force you to stop scrolling the web or make you do push-ups every time you open a browser. A drill-instructor friend that will forcefully intervene so to speak. Intervention. There is probably an addiction facility that is no stranger to cell phone additions can could help?