Step by step instructions to transfer data from both a 2012 Mcbook pro and a 2021 MAcbook Air to a new macbook air

1. Please be advised that no one on this site speaks on behalf of the Apple Community. Each person's post is his or her own and does not reflect anyone else's advice, opinions, or recommendations — including this reply.
2. Regrettably, certain inappropriate advice has been posted to this Discussion.
3. You do not need to purchase, download, or install any third-party product to accomplish what you seek.
4. Installing and using non-Apple "cleaning" apps is certain to result in the eventual need to erase the affected Macs and reconfigure them from the ground up as though they were new.
5. Duplicate files occupy zero additional space.
6. iCloud Backup does not exist for Macs. iCloud is a file synchronization service that Apple explains here: What is iCloud? - Apple Support
7. iCloud Backup exists for iOS devices and is explained here: How to back up your iPhone or iPad with iCloud - Apple Support
8. If you purchased a brand new Mac from Apple you already paid for personal, one-on-one setup assistance from an authorized Apple Support representative. Given the abysmal information already posted to this site I recommend you start with them, so that you do not have to come back here asking how to undo the damage.

To get started click the Support link below.

Hello~ Most excellent information in your post. Thx.

~Katana-San~

What kind of data is on the old MBP that is not on the old MBA?