@aqua03 hundreds. There's an absolute ton of them. Many of them are just an adjective or two thrown in front of the main subgenres. But in a nutshell, Metal evolved from Hard Rock wayyy back in the late 60s, so many early bands sound more akin to Hard or Prog Rock from that era.
Of course there are variations on those.
And then we get to the Hardcore subgenre, which evolved from Punk, which also evolved from Rock back in the 60s
And one of the newer genres actually rose from the concurrent evolutions of both Hardcore and Metal. For a long time, Metal and Hardcore were two separate scenes, but as of the 2010s, they began to solidify together. This was partially due to experimental bands and the strange love child of both sides in the early 2000s:
I'm pretty much glossing over a lot of it, because there's also many events in musical evolution called Waves that cause the subgenres to shift and change with the times and generations involved.
All that to say....there's a huge amount of subgenres, I barely scratched the surface.
Sometimes bands just slap an adjective in front of Metal, and voila, a whole new subgenre is born. For example...Ocean Metal.