The Black Hole Bomb and Black Hole Civilizations

Kurtzgesagt made a video explaining some possibilities. In short, you can throw mass or radiation at a spinning black hole and "steal" rotational energy from it. ▶ this video

There's also the Penrose process which is theoretically useful on spinning black holes. I also watched this in the past, which has some fun ideas (that are probably a little fanciful?) ▶ this video tl;dw: put a mirror around it and shine light in, get back lots of energy and/or blow up your whole solar system. I'm not sure if any of that would apply to a ~planet mass black hole spinning with ~planet sized angular momentum, or how solid the physics even is, but it sounds cool anyway.

I used to play with an idea of a science fiction novel, where the united Earth's currency is essentially kcal/kJ. The problem is that if you have a flammable and radioactive material, do you count the energy you get from it by burning it, or the energy from throwing it into a nuclear fission reactor, or the energy of throwing it into a black hole in a particular angle[1]? [1]: ▶ this video

Kurzgesagt had some nice summaries of: 1) Why white dwarves might be the last home for life in the universe - link 2) ...or maybe it will be black holes - ▶ this video