A more niche but nonetheless interesting method that I was hoping to see discussed was magnetism. Gravitational waves are expected to decay into photons in intense magnetic fields. Or so I was told by one of my physics professors back in the day. I did understand the math somewhat back then, but it is beyond me now. It does however seem as though some people are still exploring this avenue [0].

[0] https://indico.cern.ch/event/1074510/contributions/4519384/a....