Default value "nothing" in Segment with "simple selection"

Hi Sophie_ 

Agree with Syndicate_Admin.

You can create a new table containing “Nothing” with the following DAX:

SelectionTable =
UNION(
    SELECTCOLUMNS( 
        DISTINCT(yourtable[yourcolumn]),
        "Selection", yourtable[yourcolumn]
        ),
        {"Nothing"}
    )

Use the “Selection” column of table “SelectionTable” as the slicer field.

Current power bi slicers not provide the default selection value features, but you can try using bookmark: Create report bookmarks in Power BI to share insights and build stories - Power BI | Microsoft Learn

Or try using a custom visual "Preselected Slicer" to see if that helps:  How to dynamically select the default values we ne... - Microsoft Fabric Community

Best Regards,
Jarvis Tang
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.