Simple scalar group by does not work

[TehWardy]

Having been advised to upgrade from v2 because of it's end of life I notice that basically grouping is broken, the current advice appears to be to generate a ticket for grouping scenario, I couldn't find one for this scenario so here it is ...

var results = Db.Set<T>().GroupBy(i => i.ScalarValue).ToArray();

... this results in the well known issue that others reporting grouping problems are facing.
Solving this by the looks of things will fix at least 5 or 6 OData related tickets too.

Typical example from my web stack, I have an entity that looks like this ...

[Table("Resources", Schema = "CMS")]
public class Resource
{
    [Key]
    public int Id { get; set; }

    [ForeignKey("App")]
    public int AppId { get; set; }

    [Required]
    public string Key { get; set; }

    [Required(AllowEmptyStrings = true)]
    public string Culture { get; set; }

    [Required]
    public string Name { get; set; }

    [Required]
    public string DisplayName { get; set; }

    [Required]
    public string ShortDisplayName { get; set; }

    [Required]
    public string Description { get; set; }

    public virtual App App { get; set; }
}

Running this query on EF Core 3.1 breaks, but works find on EF Core 2 ...

var resources = Db.Set<Resource>()
   .Where(r => r.AppId = 1).GroupBy(r => r.Key)
   .ToArray();

[smitpatel]

duplicate of #19929