EF Core 3.1 does not allow Contains search on Enum property

I'm trying to do a contains search on enum property in my DbSet and EF Core 3.1 throws the below error

The LINQ expression 'DbSet .Where(d => d.Position.ToString().Contains("acc"))' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync()

Entity:

public class DemoEntity
{
    [Key]
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public Position Position { get; set; }
}

Enum - Position:

public enum Position
{
    [Display(Name = "Accountant")]
    Accountant,
    [Display(Name = "Chief Executive Officer (CEO)")]
    ChiefExecutiveOfficer,
    [Display(Name = "Integration Specialist")]
    IntegrationSpecialist,
    [Display(Name = "Junior Technical Author")]
    JuniorTechnicalAuthor,
    [Display(Name = "Pre Sales Support")]
    PreSalesSupport,
    [Display(Name = "Sales Assistant")]
    SalesAssistant,
    [Display(Name = "Senior Javascript Developer")]
    SeniorJavascriptDeveloper,
    [Display(Name = "Software Engineer")]
    SoftwareEngineer
}

DbContext:

public class DemoDbContext : DbContext
{
    public DemoDbContext(DbContextOptions options)
        : base(options) { }

    public DbSet<DemoEntity> Demos { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder
            .Entity<DemoEntity>()
            .Property(e => e.Position)
            .HasConversion<string>();
    }
}

When I query the table as follows I'm getting the error

try
{
    var test = await _context.Demos.Where(x => x.Position.ToString().Contains("acc")).ToListAsync();
}
catch (System.Exception e)
{
    //throw;
}

The Position is of type NVARCHAR(MAX) in my database.

This is not possible? If so please can you help me with explanation?