I though Photoshop UI scaling was a Windows preference it was introduced in CC 2014 as an experiment feature. I see it is available in my CC 2018 on windows. It is still full of issues and Adobe is working on a new implementation there is a beta test version you can sign up to test. I do not know if it includes Mac support. I never installed the beta for Adobe was not working on the scripting area that I was interested in when the beta was announced.