The expression in the label is ='[$(=_Options)]' . Options is a filed created through an inline table containing values such as "CMOP" as shown in the picture. When I put the expression ='[$(=_Options)]' in a filter pane and select a value such as "CMOP", the label changes in the filter accordingly. But when I use the same expression in the label of the dimension, it doesn't.
Also as mentioned before, the same expression works in the Title of the line chart.
Hope this helps.
The legend title just uses the text written in the dimension field label, doesn't calcaluate it like it does for title. I also had tried once in the past and realize it is designed in this way.
mto do you think we can have calculated dimension label expressions in the legend title. As of now when I put formula in dimension label, it doesn't show label at all and starts showing expression text.