How to prevent Excel file from automatically opening in OneDrive

Is there anything specific that I should look for? I saved a copy of the current sheet as a file by itself (embarrassed that I didn't think of that before; I forget to think of Excel files as individual sheets that can work independently from the file as a whole), and it worked the way it was supposed to, so I guess I'll copy each sheet to the new file one by one until I find the one with the problem, but not sure what to look for when I figure out which sheet has the issue. I can't remember what I had done just before the problem started.

Thanks!