That's usually easy to opt out of and if bootstrapping fails (e.g. Outbound dns query for DoH provider fails//direct connection by IP is blocked) it falls back to the network/OS defined resolvers.

Even still filtering based on SNI will work for a long time yet. Yes, ESNI is on track to becoming to a standard but support for legacy devices/browsers means it to will rely on network tests for support - so it can also be disabled.