Return Excel Row Indices of non-empty Cells in Column

Column with Data in A1:A20

Formula in Cell B1

=WENNFEHLER(AGGREGAT(15;6;ZEILE($A$1:$A$20)*N(LÄNGE($A$1:$A$20)>0);SUMMENPRODUKT(N(LÄNGE(Datenablage!$A$1:$A$20)=0))+ZEILE());"")

SUMMENPRODUKT(N(LÄNGE(Datenablage!$A$1:$A$20)=0)) is needed because each LEN=0 will be a smallest value, so if you have 3 cells with LEN=0 the ksmallest with k=4 will be the first non empty value..

..for details on aggregate check: https://www.youtube.com/watch?v=He3dblboncw