Table filter based on distinct value post filter based on one column - Logical

See if this works.

A) If the user is hard-coded: Create the following measure to use as a filter in the filter pane, setting the value to 1:

User 1 Plan Name =
VAR _U1 =
    CALCULATETABLE (
        VALUES ( fTable[Plan Name] ),
        ALL ( fTable ),
        fTable[Assigned] = "User 1"
    )
VAR _All =
    CALCULATETABLE ( VALUES ( fTable[Plan Name] ), ALL ( fTable[Assigned] ) )
RETURN
    COUNTROWS ( INTERSECT ( _All, _U1 ) )

B) If you need the User selection to be dynamic:

Create a new, independent table for Users (I've called mine 'Select Users"). Leave this new table unrelated in the model:

Select Users = 
DISTINCT(fTable[Assigned])

Use this measure as a filter in the filter pane and set the value to 1:

Sel User Plan Name =
VAR _U1 =
    CALCULATETABLE (
        VALUES ( fTable[Plan Name] ),
        FILTER (
            ALL ( 'fTable' ),
            fTable[Assigned] IN VALUES ( 'Select Users'[Sel Assigned] )
        )
    )
VAR _All =
    VALUES ( fTable[Plan Name] )
RETURN
    COUNTROWS ( INTERSECT ( _All, _U1 ) )

Attached is the sample PBIX file