Trees and seagrass don't really address the sequestration side though, do they?

The carbon they latch onto and temporarily hold onto is still within the land / sea surface +/- a few metres layer.

The current largest scale carbon capture projects are catching a small amount of vented CO2 from LNG projects and pushing that back into the subsurface fields - they only capture 10 ton by releasing over a 100.

We're in need of readily powered true air capture of CO2 then sequestered deep underground.

Things like www.sciencedirect.com/science/article/pii/S036031992602269X have promise.