I'm a genius.
Trying to move stuff off the Cloud, esp. Google, I made a new “Bills” spreadsheet for 2021. I spent about a half hour setting it up and formatting it. It's quite nice.
So then I pulled up the one from last year, on Google, clicked on “File” and saw the “Download” option. Went to it and it gave the option of downloading it as an .ods file.
That's the file type I used for the new one. The file type I could have downloaded and just clicked “Save As” and renamed to make a new one for this year, and not have spent a half hour making a new one from scratch...