So you have tried to open something and you get this error “This app can’t open. … can’t be opened using the Built-in Administrator account. Sign in with a different account and try again.” Don’t panic, it’s pretty simple to fix:
Right Click the Start Menu and Click Run. Type Secpol.msc and press Enter.
Navigate to Security Settings > Local Policies > Security Options > User Account Control: Admin Approval Mode for the Built-in Administrator account right click it and click Properties
Change the setting to Enabled.
Click OK and then reboot your machine and everything will be fine.
This can also be set using Group Policy for enterprise organisations.