I don’t know. Probably not bad. Large DNS providers tend to be OK unless specifically known to be not OK. Just make sure you really use DoH

Vivaldi is made by former Opera guys and deserves zero attention because it is yet another proptietary piece of crap.

Set up DoH globally for your devices if you need privacy. Something like Adguard DNS.

What do you mean no tracking since you own your own server? If you use it alone, there is a straightforward correlation between the requests from your searxng instance and you, the dude who hosts it. The idea of searxng is that requests of many people become mixed together through an instance

Searx is not the easy one. Many instances don’t work, and the working ones hardly show relevant results.

Quad9 for Quadruple Nine

Not exactly what you are asking for, but there is mitra, a microblogging service that can work through Tor and use Monero address for sign in.