How to Transfer Gmail Email to iCloud permanently?

Hey fellows, I am looking for a practical way to transfer all my old Gmail emails to iCloud, which is my new email service provider. See all the guides that I am getting over the internet are about the way to delegate access, not transfer this way. If I delete my original account, I will not have a backup. And forwarding them or downloading them one by one is not practical, as it has 2 years of emails in it. Need suggestions on how to do it