Unable to select line style and borders in timeline in excel

Hi,

I'm facinng a strange issue. I've created a timeline for a dataset and its working fine.

However, while I'm trying to edit the timeline style, it doesn't allow me to choose the border of the 'Header' element except the presets of 'None' and 'Outline', rest everything is shaded-out. The same thing is happening while trying to select the linestyle of the same. This is also happening for the 'Whole Timeline' element.

Also, the underline functionality is also grayed out while setting the font formatting.

Does anyone has any idea as to why this is happening and how to resolve it.

Unable to choose the line styleBorders grayed outUnderline grayed-out