This can't be true... I use /etc/hosts overrides in chrome all the time

In Firefox you can define those domains to be ignored, like "do not query example.com from DoH".

It works just fine on Android. I'd be surprised if desktop clients behaved differently.

The solution implies that it doesn't ignore it. At least not generally

etc/hosts doesn't scale, it came first and was replaced with DNS when we had scaling problems.

While that might be true many people still use the hosts file today to override dns resolution.

Yes, and I will say that these DOH resolver libraries ignore it is probably my number two complaint.