Interesting. I've heard about cosmological coupling before, I wonder if PBS Spacetime or Dr. Becky have mentioned this theory yet.

Showing that BH energy density stays constant, like the proposed cosmological constant, is quite interesting, but I also don't understand the leap to how that drives expansion. If vacuum energy was everywhere, I can see how that would push things apart and push harder as space grew, but if vacuum energy exists in BHs I can't make the connection to a repulsive force. Perhaps this is a event horizon resonance mode or something? Where event horizons exists for everything, and they're size and relativistic motion press upon the universe? I don't know.

Wikipedia seems to have this paper's theory listed already (here), though reception seems mixed.

EDIT: Yes, I knew I'd heard of this before. Both PBS Spacetime and Dr. Becky have fairly technical videos on this. Dr. Becky in particular does a great analysis of the paper, as the growth of supermassive BHs is her specialty.

Also, both the proposed Dark Energy and these cosmologically coupled BHs end up exibiting negative pressure in their energy. This is how more energy = more expansion. Exactly how that happens is a complicated relativistic relationship, but it's not unique to this paper.