There are some apps (like Intra) which allow you to connect to a built-in (cloudflare, google) or custom DoH server (your own or other providers which support DoH).
Nextdns have their own app for this as well.
For android 9 or higher there should be an option in network settings.
Nextdns have their own app for this as well.
For android 9 or higher there should be an option in network settings.