Report Builder | Converting DAX Query to Multi-Select Parameter

FYI, The post is for "Report Server" group. 

Based on your file, you configured the "p_Referral" as multiple values. 

1) you need to add the parameter to the dataset as below. 

    <QueryParameter Name="Referral">
     <Value>=Join(Parameters!p_Referral.Value, "|")</Value>
     </QueryParameter>

2) Change your DAX as below, in the dataset

VAR __DS0FilterTable =
TREATAS({"07072021-047", "07132021-013"}, 'IPAR'[Referral_ID])

as

VAR __DS0FilterTable =
// TREATAS({"07072021-047", "07132021-013"}, 'IPAR'[Referral_ID])

FILTER( VALUES('IPAR'[Referral_ID]), PATHCONTAINS (@Referral, 'IPAR'[Referral_ID]))

3) Optional: DAX generated by Power BI is typically huge. you can tweak it (or reduce it) to your needs.

Hope this helps!