Form submit resulting in “InvalidDataException: Form value count limit 1024 exceeded.”

The default formvalue(not formkey) limit is 1024.

Also, I think you can just change the FormOptions limit in Startup.cs file.

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<FormOptions>(options =>
    {
        options.ValueCountLimit = int.MaxValue;
    });
}