Created attachment 190493 [details]
Attachment with a trend line equation. The trend line equation decimal places format was not saved.

When creating a trendline in a scatter plot with Libreoffice Calc, adding a trend line and specifying Format Trend Line -> Numbers -> Decimal Places, this formatting is not saved when saving as an XLSX Excel 2007 file. This bug does not occur when saving the file as an ODS file. This bug does not occur when saving using 202X Excel.

Steps to reproduce:
1. Add random data (preferably with lots of decimals) to A1-A3 and B1-B3 in a new Calc file
2. Highlight these 6 rectangles and select insert: Chart. Select scatter plot, and create it as-is.
3. Edit the scatter plot, click on one of the points, and select Insert Trend Line. Select "Show Equation." Create the trend line.
4. Select the trend line equation (right click it and) select Format Trend Line Equation
5. Select Numbers, All, General and specify decimal places: 1
6. Observe that there are fewer decimal places shown in the trend line. Save the file (as an xlsx). Close Libreoffice.
7. Open the xlsx file in Libreoffice Calc (or any spreadsheet viewer). Note that the decimal places format has not been saved.

This issue can be reproduced with the included attachment starting at step 4.
Tested using Windows 11 22H2.