Sending every single query to a centralized third party is hard to square with "high privacy". I prefer to run my own local recursive resolver.
That might not be an issue for your situation, but I recall the benefit of something like Quad9’s offering is the encryption between client and their endpoint(s), particularly for untrusted ISP or similar.
Downside is Quad9 can see all your DNS traffic. But without it if you run your own recursive resolver your ISP sees all your queries, and many others see portions of them, unencrypted.
This hopefully shouldn't be an issue for long with stuff like RFC 9539 and OOTS/SVCB.
Used to be fine. I stopped doing it when average TTL dropped to 300 seconds and it takes far too long for my local recursor to get the answer >100ms, when 3rd party resolver delivers in <10ms.
cache-min-ttl: 3600 // seconds
cache-min-negative-ttl: 3600 // seconds
serve-expired: yes
serve-expired-client-timeout: 20 // milliseconds to wait for resolution before serving the old value to the client prefetch: yes