Unbound is a high-level DNS server. It needs you to provide it hosts in a list or provide it with regex scripts (for dynamic and more efficient blocking). It can block ads at the DNS level just like PiHole (because that’s literally what PiHole and AdGuard use under the hood, but add their fancy GUIs)

I would avoid it unless you know what you’re doing, and recommend reading the docs on their website and testing/breaking it within a Docker container.

It’s the difference between buying a car from a dealership (PiHole, AdGuard, etc) or building your own from scratch (Unbound). One is very limited, whereas building it and running it yourself you get to do way more than what’s spoon fed to you.