In truth BHs lose mass from more than Hawking radiation.

Some think a loss of BH mass comes from gravitation binding energy or another factor.

m=E/c2, the mass does go someplace https://www.forbes.com/sites/startswithabang/2016/12/03/ask-ethan-how-do-gravitational-waves-escape-from-a-black-hole/#18a3f3051
This question has puzzled me for a long time. Articles about LIGO discovery state that some percentage of black hole merger mass was radiated away, leaving a resulting black hole smaller than the sum of the original mergers. Yet it is accepted that nothing escapes black holes. So my questions are: how was energy radiated from black hole mergers? Do gravitational waves turn into energy from mass and propagate outwards??

Or could it be a cosmic forge of mass to space conversion?
possibly.
Over the life of the universe a cumulative 5% 'push' from more and more black holes could be the dark matter push.

To me it is a clever question but we have more questions than answers.