Please firstly ensure that you use the latest version of Synoptic Panel by SQLBI from https://synoptic.design/ . The version in the Visuals Gallery is not the latest one.
Secondly, set Legend and Values properly in the Synoptic Panel visual following the steps in this blog, bind the Legend to a Category column.
If the “Select Map” button doesn’t show up after performing the above steps, please directly contact the author. In this link, you can send an email to the author by clicking “Contact Author”.
Community Support Team _ Lydia Zhang
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.