I'm still in the stages of setting up a fullt featured firewall at home, but I wonder what would happen if you block doh/dot addresses completely in such cases. Something to try in the future when I have my home network set up properly I guess.
For DoH, you either have to block port 443 (bad idea), or block the IPs of all known DoH providers.
Then you can run for example a Pi-Hole and add a firewall rule to allow outgoing DNS traffic only for that.
And of course that will not stop device/app makers from using nonstandard ports or even tunnelling their DNS traffic through other protocols.