When using Google Sheets, there are several formulas that are specific to the Google Sheet platform that don't export to other spreadsheet programs (such as Microsoft Excel). When spreadsheets are exported with these Google-specific formulas, the value that the formula produced will be exported, but, the formula itself will not be.
But, please note that even though the exported Google Sheet does not have the Google specific formulas active within the spreadsheet, if you were to import that exported .xlsx file back into Google using the native Google import tools, the original formula would then be restored (not just the formula result/value).
Below is a list of many of the Google Sheet specific formulas that do not convert over to Microsoft Excel, when the data is exported:
Please contact support if you have any questions.