I think there is a basic problem with the support of the touchscreen under "Raspbian buster". My JavaFX application did not respond to the touch events and I thought the problem was with the application until I tested touch screen support on existing applications. Some widgets respond to touch, but some do not. The pulldowns will be e.g. is displayed, but ...
Set up a simple REST-API with PHP for example that triggers local controlling code.
You may want to add some form of authentication tho like supplying a password in the request.
A request would be along the lines of: