without `unsafe`:

using System;
using System.Runtime.CompilerServices;
using System.Text;

static class P
{
    static void Main()
    {
        var arr = new []
        {
            new NonBlittableType(42, Encoding.UTF8.GetBytes("hello")), // 42=0x2a, for later comparison
            new NonBlittableType(12, Encoding.UTF8.GetBytes("world")), // 12=0x0c, for later comparison
            new NonBlittableType(05, null), // 05=0x05, for later comparison
        };

        Span<NonBlittableType> span = arr;
        ref byte root = ref Unsafe.As<NonBlittableType, byte>(ref span[0]);
        for (int i = 0; i < span.Length * Unsafe.SizeOf<NonBlittableType>(); i++)
        {
            byte b = Unsafe.Add(ref root, i);
            Console.Write(b.ToString("x2"));
        }
        Console.WriteLine();
    }

    readonly struct NonBlittableType
    {
        public NonBlittableType(int x, byte[] obj)
        {
            _x = x;
            _obj = obj;
        }
        readonly int _x;
        readonly byte[] _obj;
    }
}