Each time I reopen a spreadsheet, the sort I had set up previously has to be continually redone. Why?
Perhaps because you didn’t save your changes?
Nope, I did save it. Thanks
You need to set up the sort for a named range.
Create the range in Menu/Data/Define range, then while inside the range define the sort criteria.
I may have recreated the problem you described (“Each time I reopen a spreadsheet, the sort I had set up previously has to be continually redone. Why?”)
I recently had a spreadsheet that remembed my previous sort criteria. Then, it stopped, and behaved has you described. My problem occured after I alter my column headings. Specifically, I used two lines within a single cell (by hitting Ctrl+Enter to make a second line). When I changed those column header cells back to single lines, sorting worked as before and remembers it between sessions.