Optimisasi portofolio saham Indonesia menggunakan cryptocurrency dan Non-Fungible Token (NFT) pada periode 1 Januari 2018 hingga 31 Mei 2022: pendekatan modern portfolio theory = Indonesian stock portfolio optimization using cryptocurrencies and Non-Fungible Tokens (NFT) in the period of January 1st, 2018, to May 31st, 2022: modern portfolio theory approach