Search value from one List of Text String to another List of Text String.

The union() function will achieve this for you:

a!localVariables(
  local!listA: {"221465","221446","221233","220867","221277"},
  local!listB: {"221465","221446","221233","220867","221277","221485","221446","221203","220867"},
  
  union(local!listA,local!listB)
)

I don't think the union() is the correct solution here - union() combines the lists together to return all the items. From the phrasing of the question, it sounds like you want the values that exist in both text strings. If that's the case, the intersection() function should give you what you need.

Totally correct sir!  Pardon my hasty reply.

a!localVariables(
  local!listA: {"221465","221446","221233","220867","221277"},
  local!listB: {"221465","221446","221233","220867","221277","221485","221446","221203","220867"},

  intersection(local!listA,local!listB)
)