Hello Wingtung531,
Thank you for using Apple Support Communities! I understand from the information you provided that you’re unable to launch the Trackpad Handwriting Window with the shortcut; I'd like to help.
To help isolate potential causes for this behavior, I suggest seeing if this continues to be an issue when you restart your Mac in safe mode:
Use safe mode to isolate issues with your Mac
If you're able to launch the Trackpad Handwriting window without issue, the next step would be to rule out incompatible login items:
If your Mac has a blue screen or other startup problems
Specifically, check out the section labeled “Test your login items”
Also, testing in another user account can help determine if this may be user or account related settings causing this issue. Here's how you can create a new user for testing:
How to test an issue in another user account on your Mac
Keep us posted with the results.
Best Regards.