When you prepare data in Multilist, there should be easier option to select them in filter preparation.
Actual:
Set up multi-list field (eg. task number for functions) and prepare TCs with these numbers.
Prepare filter with multiple values - you have separately prepare filter or you have to click "Or", "open dropdown", "select value" repeatly.

Expected:
Use shift/ctrl to select multiple values from multilist.
There should be displayed filed with selected list.
Clicking on field opens dropdown with selected values for editation of multiselection.
"X" will be over whole multiselection and delete whole selection