Other than Affinity, I don’t know who else is competing against Photoshop in the professional space. Neither have native Linux builds.
There’s also PhotoGIMP which patches GIMP to make it look like Photoshop. You can also try installing Photoshop or Affinity via WINE.
If not, why?
Neither Adobe nor Serif see Linux as a potential market. As for the open source ones, I’m guessing it’s because their funding and development team isn’t as big as an industrial giant like Adobe. I’m happy Blackmagic Design supports Linux to some degree and I get to have DaVinci Resolve on Linux natively. I wouldn’t be on Linux if DaVinci Resolve did not work natively tbh.