Difference is timescale. Coal “sequestered carbon” over millions of years, and released over a few decades.

Biomass gathers and realeases on the same timescale

Any idea where these hundreds of unused Docker volumes came from?

Yes, this happens automatically for me when I launch games. I don’t remember doing anything special to set it up (Kubuntu with nVidia drivers on X11). I do mostly game in true full screen though, not “full screened window”