How can I get the active toggle number (not value) from a ToggleGroup?

ActiveToggles doesn't return the text values, but the toggle themselves.

     group.ActiveToggles().First()

or

     group.ActiveToggles().FirstOrDefault()

Will return the first active toggle. You can then use its name, or use SendMessage to call a function on a script on it, or use an ID stored in a script on the same object, etc.

But what you usually want is to use the Toggle event list to call a function in any script (usually one on the toggle group) to set whatever setting you want.

I get the index like this:

             // Get the curren toggle group
             ToggleGroup current_toogleGroup = current_toogleGroup_gameObject.GetComponent<ToggleGroup>();
 
             // Get the selected toogle
             Toggle selectedToggle = current_toogleGroup.ActiveToggles().FirstOrDefault();
             
             // Get all individual toogles from this toogle group
             var toogles = current_toogleGroup.GetComponentsInChildren<Toggle>();
 
             // Loop through all toogles to find the one that is selected
             int toogleIndex = -1;
             for(int i = 0; i < toogles.Length; i++){
                 if(toogles[i] == selectedToggle){
                     toogleIndex = i + 1; // set toogleIndex to i + 1 
                 }
             }