Creating a Calculated Column Based on SELECTEDVALUE

1) Removed your existing inactive relationship and your calculated column.

2) Added a calculated table which lists each lender and adds an "Other Lenders" category:

Lender Grouped = 
    UNION (
        DISTINCT ( Lenders[Name] ),
        {"Other Lenders"}
    )

3) Created a relationship to your main table (you need to force it to be 1 to many:

4) Created a basic total measure:

Lender Amount = SUM ( Lenders[Amount] )

(This gets used in your normal ungrouped visual)

5) Created a measure to do the grouping:

Grouped Amount = 
VAR SelectedLenders = VALUES ( 'Lender Shell'[Name] )

VAR VisualLender = SELECTEDVALUE ( 'Lender Grouped'[Name] )

RETURN
    IF ( 
        HASONEVALUE ('Lender Grouped'[Name]),
        SWITCH ( 
            TRUE (),
            VisualLender IN SelectedLenders, [Lender Amount],
            VisualLender = "Other Lenders",  
                CALCULATE (
                    [Lender Amount],
                    NOT ('Lender Grouped'[Name] IN SelectedLenders )
                ),
            BLANK()
        ),
        BLANK()
    )

6) Swap both visuals over to use "Lender Grouped[Name]"

7) In the grouped visual replace the implicit measure with "Grouped Amount"