Unable to remove Windows Partition on Bootcamp
There are two ways.

Option 1 (recommended):

Go to Boot Camp Assistant, which is in the Utilities folder. Then click continue until you see this window:


Select "Remove Windows 10 or later version", and click continue. Follow all the steps, and it should remove it.

Option 2:

Open up Disk Utility, which is in your Utilities folder in Applications. Then, as shown in the image below, click the top left button and click Show All Devices.



Once you have done that, you should see something like this:


Click on the - sign when the windows partition is selected and click Delete.


After the process finishes, the Windows partition should be removed.