Mouse regularly freezes for a millisecond and screens 'stutter'. Very annoying   Model Name: iMac   Model Identifier: iMac19,1   Processor Name: 8-Core Intel Core i9   Processor Speed: 3.6 GHz   Number of Processors: 1   Total Number of Cores: 8   L2 Cache (per Core): 256 KB   L3 Cache: 16 MB   Hyper-Threading Technology: Enabled   Memory: 128 GB   System Firmware Version: 1554.140.20.0.0   SMC Version (system): 2.46f13