One thing suggested in another thread here is adding this to your Startup.cs:

            services.Configure<FormOptions>(x =>
            {
                x.MultipartBodyLengthLimit = 10737418240;
            });

Another possibility (also from that thread) is setting the max size for kestrel:

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.ConfigureKestrel((context, options) =>
            {
                // Handle requests up to 50 MB
                options.Limits.MaxRequestBodySize = 52428800;
            })
            .UseStartup<Startup>();
        });