I have a layer with string and numeric data (decimal).
I add a slider with Defined Values and use Integer Values (it defaults to String).
I add an integer value.
I go to Actions and select the layer and filter. My only options are String fields.
I have to Save my Selector, only partially setup.
I edit the Selector and the filter options now offer the numeric fields.
Changing the Defined Values option between String and Integer should update the fields that can be filtered.