I recently discovered there's an issue with the combination of macOS Catalina, Illustrator (at least) and 4K.
I will follow up with specs.
Same behavior with current Illustrator 2020 (24.2.1).
I just changed my color profile in the preferences from my calibration profile to Apple RGB and that did the trick!
Adding to the list in the initial post.
Still, searching for a solution since I need to work on a calibrated view.
Same issue in my case: new mac mini with the top specs, but working in illustrator / photoshop / lightroom / premiere - very very disapointing on a 5K monitor. Switching to low res or choosing only one color mode is not solution! While many apps have no problem, Adobe software fails: brand new computer, brand new monitor, brand new Adobe software = like working on very very old computer. Adobe, fix it!
same for me, very frustrating!