[Table("Settings")]
public class SettingsTbl
{
    [Key]
    public SettingsEnum Setting { get; set; }
    [Required]
    [MaxLength(20)]
    public string Value { get; set; }
}

modelBuilder
    .Entity<SettingsTbl>()
    .Property(e => e.Setting)
    .HasConversion<string>();

public async Task UpdateSetting(SettingsEnum setting, object value)
{
    await dbSet
        .Where(x => x.Setting == setting)
        .BatchUpdateAsync(x => new SettingsTbl
        {
            Value = value.ToString()
        })
        .ConfigureAwait(false);
}