So, i found the possible solution…check Compatibility Mode: Open Excel 365, go to File > Open, and try opening the file directly from the app instead of the browser. If it opens, save it as a newer format (like .xlsx) by going to File > Save As.
Repair the File: If it still doesn’t open, use the “Open and Repair” option. In Excel, go to File > Open, select your file, click the dropdown arrow next to “Open,” and choose “Open and Repair.”
Explore Advanced Features: Sometimes older files use outdated features. 101 Advanced Excel Formulas & Functions Examples from MyExcelOnline helped me update my workflows and avoid legacy features.