Restored a backup from a iPhone X 14.8 to a iPhone 12 Pro Max also 14.8. My backup was nearly 50GB. The restore took 12 hours but very happy with the outcome. Usually, I see minor hiccups, mainly missing photos/media in iMessages only. BUT this was an success. Maybe as restore backup was same exact as current OS version, it made it bug free. Useless thread, just wanted to share my experience, and that large backups CAN be reliable.