Using Classic Outlook on Windows for personal email, calendar, and contact management
If you have OneDrive backup enabled, it changes the location of the Documents folder to the OneDrive folder. You can change the .pst file location to another folder that is not synced to OneDrive or disable the backup of the Documents folder on OneDrive Settings:
Right-click the OneDrive icon on the right side of the taskbar (cloud icon) > Settings > Sync and Backup > Manage Backup > Turn off the Documents option.
This will change back the default Documents folder location but will not move the files, the files will remain on the OneDrive\Documents folder.
If you don't want to disable the Documents folder OneDrive backup, choose another folder to store your .pst files.