What should be the Arrayformula at D1 to get the column D?

Column A contains only unique value.

I have actually achieved this using two formulas:

(i) Arrayformula at B1:

={"ARRAYFORMULA 1";ARRAYFORMULA(if($A2:$A = "",,countifs(countifs($A2:$A, $A2:$A, row($A2:$A), "<=" & row($A2:$A)), 1, row($A2:$A), "<=" & row($A2:$A))))}  

(ii) Formulas at column B:

=INDEX(FILTER(B$1:B2,B$1:B2<>""), COUNTA(FILTER(B$1:B2,B$1:B2<>"")))  

(1) Why doesn't Arrayformula version of this formula doesn't work:

=Arrayformula(INDEX(FILTER(B$1:B2,B$1:B2<>""), COUNTA(FILTER(B$1:B2,B$1:B2<>""))))  

(2) I am not able to get a single Arrayformula to produce my result. What Arrayformula should I use at D1 to my desired results?

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