Dynamic slicing if string/column contains user selection

I need the ability to dynamically slice a matrix by whatever financial quarter the user selects. The issue is that our cases are logged on salesforce and a 'related quarter' is selected from a multi-picklist as these cases can often relate to multiple quarters (if the customer has a payment plan over 1 year there will be 4 quarters like:  Dec 20;March 20;June 20;Sept 20....not ideal for reporting)

To overcome this I have created a separate table with a distinct list of all the possible 'related quarter' choices. I then have a measure that searches the column of quarters and applies a value of "Show" if the value the user selected is contained. I've then put a visual filter on my table so we only see rows tagged as "Show"

You can see a similar problem here: https://community.powerbi.com/t5/Desktop/Dynamic-filtering-slicing-if-text-contains/m-p/425504

My dax (below) currently works for a normal table but NOT for a matrix (or any visual)

Dropdown = 
var mycount = 
    COUNTROWS(
        FILTER(
            VALUES('Related Quarter Filter'[Related Quarter]),
            SEARCH([Related Quarter], SELECTEDVALUE('_Customer Approvals (CAM Case)'[Related Quarter]),,BLANK())
        )
    )
return
    if(mycount > 0, "Show")

Is is possible to get a similar solution for matrices (this is a strong requirement, the matrix visual must be used)

I've attached some dummy data so you can understand how the data is structured.

Cheers