https://help.libreoffice.org/Calc/Automatically_Calculating_Series
Also called 'drag and fill'.
It's for sort lists https://help.libreoffice.org/6.1/en-US/text/scalc/guide/sorted_list.html?&DbPAR=CALC&System=Unknown%20OS and 'Sheet - Fill Cells - Series'.
Duplicate bug reporting in 113499, 143960, 143970