Rollup Fields Referencing Calculated Fields

I have a calculated field based on the following:

DiffInMinutes(createdon, Now())

When I create a rollup field on the parent entity this field does not appear to be selectable when I use SUM function.

According to the documentation I should be able to do this as the calculated field does not reference another calculated field.

So I was thinkin of using Power Automate as a workaround that means replicating how calculated fields work and scheduling it to run every couple of minutes ? ?