Scale user interface grayed out, everything stays tiny at 50% (iMac 27")

[Dominik5C60]

I have a big problem and i askes many ppl who work with PS but noone can help me. 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 a small too, but thats fine, 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. 

I found many pages were ppl report the same problem. Thats how i found out about this option above. 

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

I cant believe i am the only one out there using PS on the Mac with this problem?

Can someone help me out?

[kevin stohlmeyer]

The latest update is having issues recognizing mid-range GPUs. Try installing the previous version of Photoshop and see if the issue persists. Adobe is aware of this issue and is working on a fix. In the meantime, this is the recommended action.

[Dominik5C60]

Dear Kevin, thank you so much for your reply. I bought latest version online ... do i have to pay again or just uninstall und install ... but from where do i get the previews version and how is it working with the registration than? Can you or someone else explain or is there a link? Thank you for the support. 

[kevin stohlmeyer]

You can roll back using the following instructions:

https://helpx.adobe.com/download-install/using/install-previous-version.html 

[kevin stohlmeyer]

You don't have to pay again - that is a benefit of the cloud. "Registration" is no longer a thing- you log in with your Adobe ID and it authenticates.