Firefoxes case I think it’s disabled by default

No, it is not off by default, it is set on "Default Protection: Firefox decides when to use secure DNS to protect your privacy.".

You don’t see it, do you? First you talk about your use case but then you talk about other people. So not your use case anymore. In their use case a Pi-hole, AdGuard Home, NextDNS or whatever else maybe makes sense and isn’t a bad choice.

What happened here is: People shares their use-case, I say I don't understand why they do that, and I share my use case... I don't understand what's wrong with that... or what's your problem here. It's cool to know you are using NextDNS, it is not a self-hosted RPi that runs Pi-Hole that only works on local network.

Then you replied me with:

In my network it can only do that if the app has a hardcoded encrypted DNS server because I use NAT rules to force all unencrypted DNS to be processed by my OPNsense (which uses NextDNS as upstream DNS servers). And I highly doubt many apps even have a hardcoded DNS server anyway (no matter if unencrypted or encrypted).

Which is all super cool, but not related with what I said about Pi-Hole.

Erm… what?? Smartphones are designed for many different things. Browsing the internet is just one of many things it’s made for. It’s called “smartphone” for a reason.

Smartphones are still phones (makes call when you type a number) but smart to have a contact list, a browser, calculator... that makes it smart, like accessing to your bank with their app that normally then ensure to be safe to use, but it wasn't initially designed for that, it's not a PC (I know it can do the same, but you are forcing a small device to do something that isn't designed to do), it started without being secure by design, they needed many Android versions to start implementing security and still there is some mess with permissions. It is not designed to game, watch Instagram or stuff that makes you addicted to their content..., and then it usually gets too hot and only damages your health and the device health. Now it evolved and companies tries to make you addicted to it to collect as more data as they can to provide you some ad-targeting, while making it cheap as they can with those labor-forced works (stealing resources on other countries) to make a super-mega-fast-all-in-one device that makes you think you are a professional photographer for example, adds you fake filters... That's all bullshit, and I think this is the main reason why kids are growing so wrongly, too many shit influencers and toxic society, people living in their bubble and browsing from devices like those. Most apps require many permissions that allow to collect many data, and NextDNS does nothing about this if those apps bypass your system DNS.