I'll admit I'm not a fan of the genre really and don't know all the ins and outs but my understanding is that the '2nd wave' - those 90s Norwegian bands who did all the church burnings were kinda already sus, and obviously from that we get Varg Vikernes who is straight up fash, so it seems to me like it's something that goes back a long way.

I do like a bit of Alcest who are 'blackgaze' I think? (BM seems to create a microgenre every time someone sneezes) but yeah if I'm gonna listen to metal it's more often classic thrash, or some doom or sludge.