Personal.xlsb Workbook Keeps Opening

Ensure that your workbook is not accidentally actually saved as "Personal.xlsb.xlsm"

By default, windows hides file extensions, so you might see "Personal.xlsb" under the File Name field, but the true file type is actually some other kind of excel file (.xlsm, .xlsx, etc). I made this mistake when I accidentally forgot to choose "Excel Binary Workbook" type in the Save As... dialog when saving my Personal.xlsb.

In the Detail view of File Explorer, it should say "Microsoft Excel Binary Workbook" under File Type for Personal.xlsb. If it says anything else, you need to open it and Save As... to select a different file type.

After saving Personal.xlsb as the correct file type, I opened it back up. Go to View-->Hide to hide the Personal.xlsb workbook. Close and save. Now when I open excel, it has normal startup behavior (Start Up screen or an empty workbook depending on which options are selected).

At any time you can go to view-->unhide to see the personal.xlsb workbook and edit it.