Excell Number Format exported with backslashes (js)

Hello !

I am trying to export excell cell coming from a dev-extreme datagrid with a specific number format.

    const format = '#,00 K'
    excelCell.numFmt = format

But when I open the custom format in cells, the result is like this :
image

(I’m french so I use a french Excel version)

Thanks for your help !
Regards.