Hi @EshaVisram, in your layout, do you have a map frame? If so, you should see the map frame in the drop-down menu.
I see, so you have local or global scene and not a flat map.
You can't include a scale bar in a 3D map as scale is continuous and will change across a 3D view.
However, their is a workaround which you can try:
https://community.esri.com/t5/arcgis-pro-questions/scale-bar-in-arcgispro-layout/m-p/77862