Counting Unique Values with Multiple Criteria

and_rogynous 

Since you are using FILTER, you may have LAMBDA.  AND can be made to operate pairwise by placing it with the MAP helper function

= UNIQUE(
     FILTER(Orders[Carrier],
        MAP(Orders[Shipped],
           LAMBDA(shippingDate,
              AND(shippingDate>=start, shippingDate<=end)
           )
        )
     )
  )

Naming the Lambda functions can also be useful

= UNIQUE(
     FILTER(Orders[Carrier],
        MAP(Orders[Shipped], Betweenλ(start, end))
     )
  )

where

Betweenλ 
= LAMBDA(start,end,
     LAMBDA(shippingDate,
        AND(shippingDate>=start,shippingDate<=end
     )
  )