Perhaps you could configure more than unbound service behind a loadbalancer. Each unbound instance is configured to use different upstream dns servers.
Double check if unbound doesn’t allow you to randomly hop between dns upstreams first, but the above solution should work if that’s unavailable atm.
That is what I’m doing currently but now unbound doesn’t talk to the root servers anymore, it sends all queries to Quad9.
Both scenarios are not ideal because you always end up with one entity knowing all your queries.
Perhaps you could configure more than unbound service behind a loadbalancer. Each unbound instance is configured to use different upstream dns servers.
Double check if unbound doesn’t allow you to randomly hop between dns upstreams first, but the above solution should work if that’s unavailable atm.