❔ Unable to box custom value type

using System;
using MidiLibrary.Util;

namespace MidiLibrary.Structures
{
    public readonly struct VariableLengthQuantity
    //TODO: Override ToString
    {
        private readonly bool[][] Number { get; init; }

        private VariableLengthQuantity(long number)
        {
            bool[] binaryRep = BinaryTools.LongToBinary(number);
            bool[][] sevenBitNumbers = BinaryTools.BinaryToSevenBitNumbers(binaryRep);
            // Reverse the array
            Array.Reverse(sevenBitNumbers, 0, sevenBitNumbers.Length);
            
            for (int i = 0; i < sevenBitNumbers.Length; i++)
            {
                sevenBitNumbers[i] = BinaryTools.PadBinary(sevenBitNumbers[i], 8);
                // everything that isn't next, has a 1 (true) as MSB
                sevenBitNumbers[i][^1] = true;
            }

            sevenBitNumbers[0][^1] = false;

            this.Number = sevenBitNumbers;
        }
        
        public static explicit operator VariableLengthQuantity(long number) => new VariableLengthQuantity(number);

        private static byte[] FromLong(long number)
        {
            throw new NotImplementedException();
        }

        private static long ToLong(byte[] array)
        {
            throw new NotImplementedException();
        }
    }
}

VariableLengthQuantity a = (VariableLengthQuantity) 137;
object aa = a;