Found a way to mace a proper validation, it is a bit harder to do, but works justo show you want to.

To start with you have to terminate the \"next\" (in my case \"save\") button to don't allow saving an emty dropdown.
1. To do it, after your other form validation on actions you will need to add a new contitional action, then in the condition set: your dropdown widget state list is set and not empt.
Then if it is true you can continue with your flow, but if it is false, then you need to terminate the form:
1. To do it, you can simply use the terminate action, but I recommend adding a snack bar before telling the user that he needs to select at least one item from the dropdown.

This is how it looks:

Next is optional, but I still would do it. it is a visual color change of the dropdown it self.

To do this one, first we need to create a page state variable:
1. Simply go to the main page tree element and create a page state variable, like \"languageColorChange\" (you can name it however you want). The variable has to be a boolean, and the initial state is false, not nullable, not list.
Next, we go to the dropdown and add an \"On selected\" trigger and add a conditional action.
1. If the dropdown widget state list is set and not empty.
2. If true we set the variable that we just created to false , but if false, then we change the page state variable that we just created to true.
The last step is te easiest, now we go to the dropdown properties, and make display the colors with a condition, if the our page state variable is false, then no error colors, but if it is true, then we change the color to error colors.

I have been searching this for a while and at the end had to figurea way myself, hope this helps you out with the project. Feel free to ask me anything or suggest some changes.

[Resolved] Form Dropdown validation