When embedding math formulas (mathematical expressions created with the formula editor - aka equation editor, not calc formulas to compute data in the spreadsheet) in a calc file, if you save the file in any format (ods, xlsx, xls) and open it with Excel 2019 they disappear altogether. This is specific to Calc, since the same equations embedded in a writer file (saved both as odt or docx) are imported perfectly in Word.
Notice that with legacy LO releases (I have a 3.3 portable), the same ods file when exported in xls format (old Excel) does maintain the equations.
This is really unfortunate since very often in Calc you perform computations using some complex equation and thus embed the equation to clarify what you're doing.
At the moment, when exporting to Excel the spreadsheet loses all equations. NB equations do not even display as images or metafiles; they simply cease to exist when the file is opened in MS Excel.