Hi Kent,
My brother and I have been having this exact same issue for several months, we've been daily Apex players since launch but this bug makes it impossible to play. I had this issue when I played on my gaming laptop but since building my own PC the issue is resolved for me, however my brother has struggled with it for months. We saw this recent thread and decided to try the Clean Boot set up that you mentioned hoping there was a new fix to this. For the first 15 seconds of the first game the issue seemed resolved but immediately reverted to the old bug, where any mouse movement resulted in huge stutters and impossible playing conditions. See this clip for what happened after the "clean boot": https://youtu.be/sxVQXAnRYGM. We've also tried lowering mouse refresh rate, making sure all drivers and devices were updated, uninstalling other mouse/pointer devices, disabling the "enhance pointer precision" feature, disabling "scroll inactive windows", disabling cortana, disabling NVidia high definition audio, changing the process priority, booted as admin, turned off overlay software for Discord and Origin, and several others. Do you have any thoughts on what next step we should take? We're happy to provide any additional info that may be relevant (mouse and device model, etc)