Entity equivalent in .netcore ?

Question

My code works fine in asp.net mvc5,when i used the same code in . .netcore 3.1, the entity is not supported,plz help

public ActionResult AddOrEdit(int id = 0)
{
SELECTEDEMPLOYEE emp = new SELECTEDEMPLOYEE();
using (Entities db = new Entities())
{
if (id != 0)
{
emp = db.SELECTEDEMPLOYEEs.Where(x => x.ID == id).FirstOrDefault();
emp.SelectedIDArray = emp.SELECTEDEMPLOYEEIDS.Split(',').ToArray();
}
emp.EmployeeCollection = db.VIEW_USER.ToList();
}
return View(emp);
}