When I set the proof set up to sRGB, no matter what I do with the image, the out of gamut warning is grayed out in the menu. I work with Nikon .NEF files in Adobe RGB and ProPhoto RGB color spaces. If I switch proof set up to CMYK, out of gamut warning is not grayed out and PhotoShop shows out of gamut colors. As I increase saturation out of gamut color regions grow which makes sense. But when I switch back to sRGB proof set up, no matter how much I saturate colors out of gamut warning is still grayed out. PhotoShop release is 22.4.2.
Yes, but obviously it should work for sRGB too, as long as the file is in a color space bigger than sRGB. Not at my workstation to test now.
All that said, gamut warning is pretty useless because it doesn't tell you howmuch. Soft proof is much more practically useful, although it does require a wide gamut monitor, preferably covering the document color space in full.