So i have Pi-hole + Unbound setup in my Raspberry Pi , and i was wondering if i can add Stubby to use with my setup ?
What are you trying to achieve? When I moved to unbound, I abandoned using stubby + cloudflare. There is no need for it.
i was doing some research , and saw that you can use stubby + Pi-hole unbound at the same time, the purpose it to have DNS querys encrypted.
You don't need the added complexity of running them both. Unbound has the ability to run as a forwarding resolver, sending it's queries via TLS to an upstream provider.
Note there is no normal benefit to encrypting your DNS queries, and unbound is more private in recursive mode.