Are the Mac mini’s UHD graphics powerful enough to run Photoshop?

TL/DR.

Yes. The Mac mini’s UHD graphics work just fine in Photoshop.

My testbed:

Mac mini (6-core i7 processor), 32GB RAM, 256GB built-in SSD
300GB dedicated Photoshop Scratch Drive attached via USB3 hub to the Mac mini
Wacom Cintiq 27QHD
Adobe Photoshop CC 2019

My test file was a blank 11″ x 17″ canvas with a 600 pixel per inch resolution.

What I tested:

Canvas rotation
Canvas zoom
Painting with large (1400px) and small (6px) custom textured brushes from the Kyle Webster Megapack

For an 11″ x 17″ canvas, I noticed a slight delay when selecting a new brush and using it for the first time, but this goes away within milliseconds of using it. On smaller files (I typically use 4000px x 4000px @ 600dpi) there were no loading issues whatsoever. There was no lag while actively using brushes on either file size. There were no issues in manipulating or editing images with the UHD graphics processor in the Mac mini. In short, it should suffice for everyday Photoshop work.

Side note: I’ve been using dedicated Scratch drives for big applications like Clip Studio Paint and Photoshop. Scratch drives act like virtual memory, should you exceed the RAM size while working with a large document. I strongly recommend a dedicated scratch drive (preferably USB 3.0) directly attached to the Thunderbolt3 port on the back of your Mac.