.Net 6 is requiring all non-nullable fields when I try to deserialize JSON

I'm converting an app from .Net standard to .Net 6, but my controllers are throwing errors if I don't pass in all non-nullable fields. e.g.

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string CustomerType { get; set; }
}

When I try to pass that object to an action without one of the fields, it throws an error like "The FirstName field is required." How can I get around that? I'm using NewtonSoft via the startup file like this:

builder.Services.AddControllers()
    .AddNewtonsoftJson(options => 
    { 
        options.UseMemberCasing();
    });

builder.Services.AddControllersWithViews()
    .AddNewtonsoftJson(options =>
    {
        options.UseMemberCasing();
    });

The easiest way is to open a project configuration file (just click on project name in a VS solution explorer) and remove option nullable

<PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <Nullable>disable</Nullable>   <!-- change from enable or remove --> 
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

or if you want to disable nullable check only in the controllers actions, you can try another option:

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