Good day,
Thanks for your post in Microsoft Community.
It seems that there maybe something wrong with your profile, please try create another admin account to check the issue.
Press WIN+X, run PowerShell as admin, insert the command and press enter.
net user test /add
net localgroup administrators test /add
Login with the new test account and check if the checkbox is off.
Feel free to post back if you need further assistance.
Best Regards,
Silvia | Microsoft Community Support Specialist