Sharepoint - Calculated column to show status if another has a value

try the below formula, add the below formula in the status - calculated column

=IF( ISBLANK([completed]) , "Open" , "Closed" )

Try using below formula, it will work for you:

=IF(ISBLANK([completed date]),"Open","Closed")

Note:

1. Sometimes comma(,) does not work in formula (I am not sure but it is based on something language or regional settings on your site). So in that case use semicolon(;) instead of comma(,).
2. Return your calculated field as Single line of text.

Example:

Column Settings:

Output:

official documentation:

1. Calculated Field Formulas.