After my test, on ?macOS 10.15.7 Catalina?, the answer of ?Dom / Rikin Patel? cannot recognize the [.xlsx] file normally.
I personally summarized the practice of most of the existing answers and passed personal tests. Sum up the following answers:
accept=".csv, .xls, .xlsx, text/csv, application/csv, text/comma-separated-values, application/csv, application/excel, application/vnd.msexcel, text/anytext, application/vnd. ms-excel, application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"