Scale user interface deactivated but required to change, everything 50% a Mac 17"

[Dominik5C60]

I have a normal iMac (Big Sure, 27") and i bought the latest PS view days ago. Now, whatever i open, no matter if its one of my PSD Web-Layouts, a new RAW-Photo or just a new plain document, all the pictures are very tiny. The toolbars doesnt seem to small. But all pictures open like 50% of the size. If i zoom them to 200% they are 1:1 for the screen as they used to be with my old PS for many years.  For example my web-Layouts are 72 DPI and they used to be 1:1 the size in PS and online. 

The option "Scale user interface" at the main settings is deactivated and i cant choose anything. As i found out THIS is the option i need to change to 200% to make the documents open with 1:1 screen size. But how if this is not activated? I simply cant use PS that way when all pictures are that small. 

Still running the 7 days test-version. Does ist unlock when i buy it? (makes no sence to me, but maybe?)

Can someone help me out?

[kevin stohlmeyer]

The latest Photoshop build has issues with recognizing and using mid-range graphic cards. This would cause this issue. Revert back to a previous build of Photoshop for now until a resolution is posted in an update.