Measure For Last Invoice Date by Customer?

I have been asked to provide the last order date for each customer in a Power BI report. I am connecting to an existing semantic model, so I am unable to edit the model in Power Query or add a calculated column to the semantic model. I was hoping to accomplish this through DAX in a measure. What I believe to be the relevant information is as follows:

Tables:
factSales - shippingCustomerKey (integer), invoiceDateKey (integer, assigned as YYYYMMDD)
dimCalendar - dateKey (integer as YYYYMMDD), calendarDate(date, MM/DD/YYYY)

dimCustomer - customerKey (integer), customerNumber (text)

Relationships:
factSales[invoiceDateKey] * : 1 dimCalendar[dateKey]

factSales[shippingCustomerKey] * : 1 dimCustomer[customerKey]

Example Data:

factSales

dimCustomer

I don't think dimCustomer is directly relevant, but including it anyway in case it is

dimCalendar

Desired Output:

In looking through these forums, I found the accepted solution here (https://community.fabric.microsoft.com/t5/Desktop/Create-a-max-date-measure-for-each-id/td-p/2992029) and modified it as follows:

lastInvoiceDate = 
VAR _dates = ALLSELECTED(factSales[invoiceDateKey])
VAR _result = CALCULATE(MAX(factSales[invoiceDateKey]), REMOVEFILTERS(factSales), VALUES(factSales[shippingCustomerKey]), _dates)
RETURN _result

In my opinion, this works great as it outputs the factSales[invoiceDateKey] that corresponds to the most recent invoice date for each customer. However, during testing, the business users requested that this be converted into MM/DD/YYYY format. I initially tried changing the data type of the column, hoping that Power BI would recognize it as a valid date format, but all I got back was the text representing the date format I selected (e.g. instead of displaying 20080402 as 4/2/2008, it displayed MM/DD/YYYY). I tried parsing out the year, month, and day from _result and forming a string with "-" or "/" as separators and received an error (using too much memory I believe). Same result when I tried to parse those values and put them into DATE to form an actual date. I also tried using ADDCOLUMNS to modify my factSales table to include a column that parsed the invoiceDateKey into a date, but I couldn't figure out how to use it later.

Is there anything else I can try in order to return a date or a string in a mmddyyyy format with / or - as separators? I'm a novice with DAX and my attempts to pull back the date from my calendar dimension were fruitless. Any assistance would be greatly appreciated. Thanks in advance!

-Tom