Hello! My name is Mustafa, and I am an Independent Advisor as well as a long-time Microsoft user. I'm sorry that you are experiencing this issue, and I am hopeful that I will be able to help you find a satisfactory solution.
Unfortunately, it is not possible to do so. Even though that part of the screen has broken the window still detects it and counts it as part of your screen size.
And there is no setting to make your device work only until a certain part of the screen.
Please let me know if this doesn't work or if you need further assistance.
Warm Regards,
Mustafa