You could use 'Button' with 'Apply bookmark' action, bookmarks will be for different countries selected and respective countries flag could be used in image. Reference video- https://www.youtube.com/watch?v=5Ws7ws2aSWk
If the issue is solved please mark the answer with Accept as Solution
Thank you for the solution. I have tried using button action but I would like to have a cumulative selection.
When I use a bookmark or a specific value selection. I can only select one country. I would like to have the possibility to add a country to the current selection by cliking on the button. For example I clik on the Germany button then I clik on the USA button and I will have in my field selection (Germany and USA) not only the last I have clik on.