Hey again! We’re you able to try the other steps in the article? (Safe Mode, Check the adapter, etc)?
If those don’t make a difference, I’d probably create a new admin user, log into that user and test, it could be just your user profile permissions are corrupted, or there is some app/login item launching upon login, and/or a corrupt setting or preference.
But I guess another valid question before all that, is does the same happen at the login screen, even before logging in? If so, then most likely will also happen in a new user, and could be either HW or an OS issue.
If so, and safe boot makes no difference, and known good mice/keyboards have the same issue, I might run diagnostics, and if all says good, may still try reinstalling the OS from recovery mode.
Safe boot and test admin user are good ways to narrow it down though, (And testing with other devices if possible). Best of luck!
Safe mode:
https://support.apple.com/en-us/HT201262
Run hardware diagnostics:
https://support.apple.com/en-us/HT202731
Reinstall the OS:
https://support.apple.com/en-us/HT204904