Is your Eraser functionality not working when you draw a shape using the Wacom pen and then flip the pen to use the Eraser tool?
This issue occurs only when you use the latest Wacom driver 6.3.37-2 with macOS 10.15 (Catalina). It can happen when Illustrator's control over TabletDriver is disabled in the macOS privacy settings.
Do you find the pressure-sensitive options grayed out in the Brush Options dialog?
To confirm the issue, check keyboard shortcuts with mouse instead of Wacom pen.
It's known issue with Wacom's latest driver, 6.3.34. Check release notes.