Hi Rainer,
yup, I have a “déjà vu” 
Some call it consulting some product development…
18 years in automotive …
In old times I wrote code,
Now there are build pipelines, automated tests, code scanners, and a lot more,
Sometimes I miss the old times, where you had to think twice to start a cleanbuild and were testing your software with pencil and paper. But what I really don’t miss : big endian little endian, word length on embedded systems without any debugger ( don’t use println, this will cause task switches and slow down the kernel…)
BR Rainer
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is there a free way to write an .xlsx File plain from sratch?
you know? you can rename it to .xlsx.zip
and if you open it you see xml files 
one free classes to write an excel file
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But xls only, right? But good catch anyway and great response for the OP.
I forgot about that page. Great stuff at that time, it is a pity that there seems to be no further development.
yes and it’s a little old it’s realstudio stuff but anyway still usable.
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anyway still usable.
The XLS file created is in XML format that can be read by any Excel application (Windows or Mac) available since 2004.
Pretty sure I tried that library myself a month or two back, but the resulting file wasn’t understood by Numbers on the Mac, or Excel on my work laptop.