=LET(Data,verticalArray,
SCAN(0,Data=DROP(VSTACK("",Data),-1),
    LAMBDA(a,b,IF(b,a+1,1))))

This formula works well for a vertical array, but I can’t formulate a working counterpart if the dataset was horizontal (e.g., A1:Z1).

The intended result is to replicate a COUNTIF(A1:Z1, A1) formula and return an array (note that COUNTIF(A1#, A1) does not work, and COUNTIF($A1:A1, A1) copied across is not an array.

Attempted but failed:

=LET(data, A1#, SCAN(0, data=DROP(HSTACK("", data), -1), LAMBDA(a,b, IF(b, a+1, 1))))
=LET(data, A1#, SCAN(0, data=TRANSPOSE(DROP(VSTACK("", data), -1)), LAMBDA(a,b, IF(b, a+1, 1))))
=LET(data, A1#, SCAN(0, data=DROP(TRANSPOSE(VSTACK("", data)), -1), LAMBDA(a,b, IF(b, a+1, 1))))