Forests do net sequester carbon. But if you want to really sock away the carbon you harvest the trees and pyrolize it. It will give you energy (heat) you can use and elemental carbon (biochar). You could bury that a few feet under or innoculate it with microorganisms and work it into fields. Carbon in that form will sit in the soil for hundreds of years. Thousands or millions if you bury it.

I mean technically we already do this: renewable plantation timber is a widespread operation (also why I get kind of annoyed at YouTubers talking about how great the timber is in old homes - yes it's great because it was logged from 50 year old old growth forests and now they're all gone because we cut them down).