Why is ASP.NET Core saying my form field is required even if it's not defined as required?

I am using .NET 6 with Fluent Validation and I have a form with the field:

<form method="post" asp-controller="Product" asp-action="Create" asp-antiforgery="true" autocomplete="off">
    <label asp-for="Description">Description</label>
    <input asp-for="Description" type="text"> 
    <span asp-validation-for="Description" class="error"></span>
    ...
    <button class="submit" name="button">Create</button>   
</form>

The ProductModel is:

public class ProductModel {

  public String Description { get; set; }

  // ...
}

And the ProductModel Fluent Validator is:

public class ModelValidator : AbstractValidator<ProductModel> {

    public ModelValidator() {

      RuleFor(x => x.Description)
        .Length(0, 200).WithMessage("Do not exceed 200 characters");
    
      // ...

    }
}

When I submit the form I get an error on description if I let it empty:

The Description field is required.

But my validator is not requiring the description.

This happens to all fields. When not filled I get a similar error.

What am I missing, and how can I make it not required?

This seems to be due to a problem relating to model validation changes; specifically in .NET 6. I found a documentation link that can explain it better than me but I'll give a code implementation also: Microsoft docs

builder.Services.AddControllers(
    options => options.SuppressImplicitRequiredAttributeForNonNullableReferenceTypes = true);

//Removes the required attribute for non-nullable reference types.

I've taken this code straight from the MS docs, so if it doesn't fix your issue, there is likely another cause.