Ruler with "pixel dirt"
I've noticed this "pixel dirt" at the base of the upper ruler. Sometimes, it shows up, I quit and it's gone to later show up again, "out of the blue".
InDesign v. 16
iMac (Retina 5K, 27-inch, 2017), 64GB RAM. MacOS 10.15.7
Brad Fischer commented
Same issue. 27" iMac Retina 10.15. Happens in v16.4 on randome files, but also v15 if file is saved as IDML.