I see plenty of people just adding it to their hosts file blacklists / DNS overrides like they do for other ad and malware domains, such that it resolves to a bad IP like 0.0.0.0. That's not what you should be doing in this case.
> The use of this domain is specified by Mozilla, as a limited-time measure until a method for signaling the presence of DNS-based content filtering is defined and adopted by an Internet standards body.
Presumably that'd be the IETF, and I have no idea which committee would be working on this, if there's a draft RFC in the works, etc. But it's clear the expectation is some sort of standard mechanism will eventually replace the canary domain that yields the same functionality but in a less hacky way.
There's also [3] which is a way for the DHCP server to also provide DoT and DoH servers to the LAN (in addition to the usual DNS servers).
[1]: https://datatracker.ietf.org/doc/draft-pauly-add-resolver-di...
Edit: I forgot, as another commenter pointed out, they also have a canary domain (use-application-dns.net) that you can blackhole to disable this at the network level (unless the user manually enables DoH).