Ok to those whos interested in a solution I found a way around to be able to pass values to pop up fields - my solution is custom made for my purposes, but you can work on it and fit it to your needs:
The solution:
1. Open the link options of the button after your popup is selected.
2. Decide which parameters you want to pass, in my case I used a custom parameter named "country" to pass the custom value of the country within it.
so the custom parameter in my case was country|myValue (country|spain)
3. Add the country field in the pop up:
a. Give the field your custom ID in the advanced section - in my case it was customCountry.
b. Set the 'Default Value' as a Request Parameter, set it to Get Option, and add your custom parameter name - In my case it was country.
4. add this custom script to your specific page you have these custom buttons on (I know I could have added more validations for the eventListener, but this is something I created fast and it does the work - It might break other things though, so try to keep it only on the relevant page if you are not planning to change it)
I used Google Tag Manager to implement this script, so I have the ability to control on which pages it will run. you can probably find other solutions too. (this is also why the script is using var instead of let and normal function instead of arrow function)
<script>
window.addEventListener("click", function(e) {
var z = e;
document.getElementById("form-field-customCountry").value = z.path[2].attributes.country.value;
});
</script>
Let me know if you have any questions about it.