As far as I can remember one could select "out of gamut" in the Select -> Color Range dialog. This option is gone for me in Photoshop 23.2.0 on a Mac. I have select "Proof Colors" and "Gamut Warning". Please see the attached screenshots.
I hope this helps neil barstow, colourmanagement net :: adobe forum volunteer:: co-author: 'getting colour right' google me "neil barstow colourmanagement" for lots of free articles on colour management