I'm using LR 9.2.1 on a 2019 iMac running Mojave OS. I'm seeing large random areas of color and black artifacts scattered all over the image. They are present in the library and develop module and persist at every zoom level and when opening into PS. I've looked through the forum and online. I've uninstalled and reinstalled LR and PS. I've tried to update to the latest OS (Catalina) and can't, with extensive help from Apple Support, including reformatting the hard drive. Still no fix. RAW files from the SD card imported onto LR (v. 7.5) on my laptop display normally. See screen shot of RAW file and then a quick editted JPG. My next step is to try to install an older version of LR. Any other suggestions?