You have a new iPhone or iPad—congratulations! When transferring your data to the new device, you have three options: Quick Start, an iCloud backup, or a Mac backup. All will work, but they don’t quite provide the same end result (particularly if you didn’t encrypt your Mac backup). My advice—backed by this post from Apple expert John Gruber—is to try Quick Start first because it transfers everything directly from your old device to your new one, maintaining app logins in most cases and allowing you to transfer your Apple Watch pairing. It tells you that this may take a little longer, but it's taking longer because it's transferring more, and not relying on iCloud.
Quick Start setup works with an old device running iOS 11 or later, or iPadOS 13 or later. The direct device-to-device transfer recommended here requires both devices to have iOS 12.4 or later, or iPadOS 13 or later. Update both devices to the latest software they support, turn on Bluetooth, connect the old device to Wi-Fi, and follow Apple's instructions in the link above. Keep both devices nearby and connected to power during the transfer.
