Can I please have instructions on how to update my MacBook with an external device........my Mac doesn't have enough space left to go from Catalina to Monterey and Apple is messaging me to say it will no longer be supported.
MacBook Air 13″, macOS 10.15
Get an external HDD or SSD, format it, make sure Laptop has AC power...
Start up from macOS Recovery
Option-⌘-R
Upgrade to the latest macOS compatible with your Mac.
Choose external drive or SSD to install to, then after install on 1st boot on the external drive, use Setup Assistant to copy all your stuff to the new drive.
PS, during install your Mac will restart up to 7 times, be patient.
Will I have to keep the external drive attached all the time after I do this?
Yes, unless it allows us to fix the Internal drive, but there are pretty small drives, like..
Instructions : how to update Mac on external device
