Excel file lost several days of changes, is anything recoverable?

did you open it from an email attachment? if you opened it straight from Outlook and kept saving, it was saving into a hidden temp folder, not where you think. search for a folder called Content.Outlook under AppData\Local\Microsoft\Windows\INetCache, the days of work are sometimes sitting in there. also worth a look in AppData\Roaming\Microsoft\Excel for any autorecover files.

Depends a lot on where the file lives. If it's on OneDrive or SharePoint, you're probably fine: File > Info > Version History lists the saved versions and you can open any of them side by side. If it's a local file, try File > Info > Manage Workbook > Recover Unsaved Workbooks, then right-click the file in Explorer > Properties > Previous Versions. That last one only has something if File History or restore points were switched on. If all three come up empty, I'd be honest with yourself that the days are probably gone. Don't keep saving over the file while you look, though.