If you made an exact clone of Photoshop
Yes but you wouldn't actually need to make your clone very different for the copyright to be entirely different and then surely you wouldn't get sued? And I think in this case, it is definitely sufficiently different, it's a completely different tech stack and while the UI is similar, it's probably not identical (I haven't checked though). But also you can't really copyright UI beyond the design itself, the functionality is free game as far as I understand.
Also worth remembering that different countries may have different stances on this. I'm curious how the EU might handle it.