What I would suggest is to create a non-persitable dashboard entity that contains this dropdown and other filters and will be the Parameter (or use a data source microflow creating the object, depending on how you will navigate and what the required functionality is) of your dashboard page.
If you place the charts inside of the context of your dashboard object, you can use conditional visibility on the charts referring to the filters, or if you place them inside a layoutgrid, you can use the dynamic classes for the column to show/hide it (including the entire content). The statement would be something like if $DasboardObject/ShowGraph = false then 'hidden' else ''
Hope this helps