The above is a simple operation. Ive done it before (Ive have been using spreadsheets for over 30 years) LIbre office help has got to be th most unfriendly help I have ever used.
Seach is almosts useless: searching column gets me into test fucntions. When I press F1 in calc and i epect to get Calc help.
Would Window - Freeze be what you’re looking for?
https://help.libreoffice.org/Calc/Freezing_Rows_or_Columns_as_Headers