Sorry, but UI scaling in Photoshop's Preferences doesn't work (yet) with Macs, as I understand it. Apple uses a different scaling system from Windows. The best you can do is set the text to Large in Preferences and restart Photoshop. Maybe someone more knowledgeable can explain why we can't use that feature on a Mac.
Apparently though, according to a thread Jeff Tranberry participated in:
"The solution on the Mac is to go to System Preferences > Displays... and choose the "Scaled" radio button and choose a setting on the "More Space" side." Or perhaps you need the "Less Space" side. I can select "Scaled" on my Mac, but then I just get a list of resolutions for my monitor. I can pick a lower resolution to scale larger.