Using NVarChar in asp.net core

Try this:

Column(TypeName = "nvarchar(MAX)")]
public string Bucket { get; set; }

You can use the attribute as suggested by @JOSEFtw but it's also possible to do with the fluent API if that's how you're defining other properties.

modelBuilder.Entity<YourType>()
                    .Property(p => p.Bucket)
                    .HasColumnType("nvarchar(max)");