We've discovered a Mac Display setting called ProMotion may be causing the viewport to glitch on some Mac systems. Not all Mac systems have this feature, but if it does, choosing another option may help.
To start, head over to your System Preferences > Displays settings. There you should see ProMotion as the selected Refresh Rate option. Hit the Dropdown menu and choose 60 Hertz.
Once complete, open Cinema 4D and see if the issue has been resolved.
If disabling this feature does not solve the issue, please open a support ticket with the following link and let us know!