Last time I looked into this trying to get PiHole working on my TV, I found an article that said some TVs give you the option to override the DNS but on the code side it just completely ignored the manual DNS change.

Depending how much control you have over your network, you can defeat this. I have my OpenWrt router configured to block all port 53 traffic unless it comes from the PiHole or router itself. You could also do redirects with masqing I suppose.

Fails if they’re using DoH, but older gear isn’t going to have that functionality built in yet.