Database temporarily generate and increment Id

[MG1376]

this is part of my base entity:

 public abstract class EntityBase
 {
     [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
     public int Id { get; set; }

still I need to set a unique Id in my entity so that it can be added and saved, While this feature is what I want (since I want to sync with my server and save server generated items locally), Occasionally I want to add an item and database generate an Id.
is there any EF core and linq way to do this?