On android, I use rethinkDNS. Its pretty configurable and open-source.
On windows or linux, I use mullvad dns. They have 2 free DNS resolvers(unfiltered, adblock)
There is free DNS resolvers on mullvad. Check it out here.
You have to be careful since these DNS resolvers are different to DNS resolver which mullvad VPN uses. If you are not using mullvad VPN, those would be fine. But if you are using mullvad VPN, consider other.