FILTER function with a What-if Parameter

Hi nonononogin 
Calculated tables cannot read the filter context, therefore, this approach is not going to work.

Altenatively, create a compy of the table visual, then you can create a filter measure as follows, place it in the filter pane of the copy table and select "is not blank" then apply the filter

Filter Measure =
COUNTROWS (
    FILTER (
        'Table A',
        [COMBINED_SCORE] < AVERAGE ( 'Table C'[Threshold Score Value] )
    )
)

Note that I have used AVERAGE for aggregation in case the user selected multiple values then the [Combine_Score] measure will be compares to the average of the selected values. You can choose another aggregation like MAX or MIN based on your requirement or you can just use SELECTEDVALUE in which case the measure will be compared with BLANK in case of multiselection and the filter will therefore return all -ve results (In your case no results)