Currently, the only way to configure DoH for everything is one-time setting local dnscrypt-proxy as the only resolver. Easy on Android 9+ and Linux with systemd, on Windows you have to override DNS settings for
all NICs because it has a weird process of resolving. Don't know about macOS, iOS is definitely out.
edit P.S: I'd never trust ISP's DNS servers, because it's the easiest way to track what customers does.