New macOS Catalina 10.15.7 update fixes 27-inch iMac graphical corruption issue
An update to macOS Catalina incorporates bug fixes for some users, but perhaps more importantly resolves an issue that manifested in graphical issues on the 27-inch 2020 iMac.
The graphical issue was reported around August 31, and accounts of issues first started popping up on Apple's support forums. There was little consistency between trouble reports, and the problem didn't seem to manifest just during intense workloads, and even appeared when the impacted iMac was idle.
Not every user saw the issue, but the problems were mostly focused on the iMac with a 3.6GHz 10-core Core i9 processor, 32GB of memory, and AMD Radeon Pro 5700 XT 16GB graphics. AppleInsider was not able to reproduce the issue.
The update also includes some fixes issued with an interim supplemental update for Catalina, published for select machines earlier in September.
The update is available in combination versions from any Catalina version, and "delta" updates through Software Update for 10.15.6 users. It arrives in conjunction with security updates for macOS High Sierra.