I can only imagine that a recent windows update installed on your computer may have caused the issue. Always back up and create restore points before installing new updates. You will still be able to access your third-party applications with the new account unless they are installed per profile.
You can try the method below to see if this fixes the issue with your main account.
Login to the new user account
Open File explorer then Under View > Show hidden items
Navigate to this folder
C:\Users\username of the main account>\AppData\Local\Packages\Microsoft.Windows.StartMenuExperienceHost_cw5n1h2txyewy\Settings
Delete all files inside
Once deleted, restart your computer then login to your main account.
If this does not work, please do the same in the following path below
C:\Users\username of the main account>\AppData\Local\Packages\Microsoft.Windows.ShellExperienceHost_cw5n1h2txyewy\Settings