Hey @Karol-W
"Data source Cloud Backend" is to configure which datasources are loaded on the page (don't load too many or your page will be slow)
"Triggers ->Cloud Backend" is to configure an action that will call a cloud backend function
Dynamic datasources are useful to generate pages based on url parameters, they are useless for this kind of interaction you want to do here.
So I would recommend you to remove that data source and replace it with a regular API call instead
We have more tutorials about generating dynamic content without dynamic datasources here: https://support.appdrag.com/doc/Creating-Dynamic-content-using-Factory
https://support.appdrag.com/doc/Creating-Dynamic-content-using-Visual-Factory
here you have a dropdown and you want to change the gallery content when the dropdown value is changed, so you should write some jquery code to capture the change on that SELECT dropdown
$( "SELECT[name='YourSelectNameHere']" ).change(function() {
var newVal = $("SELECT[name='YourSelectNameHere']").val()
//Call your function to load data from the api and display it
});