entity framework configuring foreign key in one to one relationship

Question

I have two tables products and relationships.

Product:

public int Id {get; set;} //primary key
public string Name {get; set;}
public int Availability {get; set;}

Relationship:

public int Id {get; set;} //primary key
public string RelationshipName {get; set;}

Primary key of Relationship table to be set as foreign key in the Product. It is a one to one relationship. For entity framework core to generate migration, I have added a new property in both the tables as below

Product:

public int Id {get; set;} //primary key
public string Name {get; set;}
public int Availability {get; set;}

/// Added new property
public virtual Relationship Relationship {get; set;}

Relationship:

public int Id {get; set;} //primary key
public string RelationshipName {get; set;}

///Added new property
public virtual Product Product

RelationshipConfiguration is as below:

public void Configure(EntityTypeBuilder<Relationship> builder)
        {
            builder.ToTable("Relationship");
            builder.HasKey(x => x.Id);

            builder.Property(x => x.Id)
                .IsRequired()
                .HasMaxLength(DataConstants.KeyStringLength)
                .IsRequired()
                .IsFixedLength()
                .HasValueGenerator<SequentialGuidStringValueGenerator>();
        }

Product Configuration is as below:

public void Configure(EntityTypeBuilder<Product> builder)
        {
            builder.ToTable("Product");
            builder.HasKey(x => x.Id);

            builder.Property(x => x.Id)
                .IsRequired()
                .HasMaxLength(DataConstants.KeyStringLength)
                .IsRequired()
                .IsFixedLength()
                .HasValueGenerator<SequentialGuidStringValueGenerator>();
                
                //how do I set the foreign key configuration with relationship here
        }
    
    

1. How to set the foreign key configuration with relationship in Product table? Need to set HasOne, WithOne, ForeignKey Relationship in Product Configuration? Should it be

   builder.HasOne(x => x.Relationship) .WithOne(x => x.Product) .HasForeignKey(x => x.Id);

// but this lead to having no property in Product to hold the foreign key value of Relationship

or

do I need to add another property in Product like

public int RelationshipId {get; set;}

and the configuration to be

builder.HasOne(x => x.Relationship)
               .WithOne(x => x.Product)
               .HasForeignKey<Product>(x => x.RelationshipId);

Can you please suggest what is the approach for configuring one to one relationship? And also adding a new property in each table the right approach?

Thanks in advance.