Newbie here, what kind of metal is this??

Looks like old iron. The holes and divots are blisters from the metal separating with rust and corrosion. If you look close theres that wood grain texture. Rust blisters start in there and expand out.

Might try electrolysis?

Is it magnetic? If so you ruled out brass, copper. Smell it, sometimes you can smell the metal/iron/rust smell. It looks very fragile so any cleaning including electrolysis will probably ruin it. Aim for stabilizing it from further damage. Hot wax is one option.

Some have soaked their item in molasses for a long time. There is a more gentle chemical process in play. You can google it.

(I know this because I ruined good iron spikes in the same condition as well as a carved wedding band from a shipwreck)

This is a good article and please search for others…
https://www.patriotrelics.com/how-to-clean-iron-relics

That is a nice buckle.