Detect if Android screen is widescreen?

i'm not exactly sure what you mean by widescreen but you can check the orientation of the screen using:

 Screen.orientation

here re:

 using UnityEngine;
 
 public class ExampleScript : MonoBehaviour
 {
     void Start()
     {
         Resolution[] resolutions = Screen.resolutions;
 
         // Print the resolutions
         foreach (var res in resolutions)
         {
             Debug.Log(res.width + "x" + res.height + " : " + res.refreshRate);
         }
     }
 }