Hello @Timbo ,
you can't use Filter Query on a calculated column, but you can move the whole calculation into Power Automate. The calculated column is the Agreement Date + Duration Value, the same calculation can be done with the addDays(...) expression.
addDays([AgreementDate],[DurationValue])
Note:
replace both the values with the dynamic content representing the columns
similarly, if you want to check if today is the expiration date based on the AgreementDate:
AgreementDate eq 'addDays(utcNow(),-[DurationValue])'
Note:
replace [DurationValue] with the dynamic content representing the column