I just upgraded to Catalina, and while the photoshop tools in the iPad work okay, if you drag in hi-res or large photoshop files into the ipad, you'll run into display issues such as not zooming correctly, slow movement, incorrect layer display, among a few others. I'm not sure if it has to do with transmission (large files back and forth between bluetooth/wifi), and since I don't have a USB-C to Lightning adapter, I can't determine another possibility. Although working on Adobe Illustrator files have been no problem. I suspect its a large file issue.
I have the same issue.My device is MBP(16inch i9 5500M 10.15.5)and iPad Air3(iPadOS 13.5.1).It happens in both Photoshop 2019 and 2020.And I have an USB-C to Lightning adapter.But the same issue still happened.I don't know if it's a OSX Catalina problem or Adobe problem.It's really bother me.Especially the zooming issue.