Hi,
I suggest you go to this location:
%AppData%\Microsoft\Spelling
Please check if you have 10 custom dictionaries in the folder, try to remove One(back up the folder) and check the result.
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.