Should upgrade my 2018 Macbook pro that is still on Monterry before I migrate on to my new MBPro ? Planned to use my external Time Machine drive but not sure how it will work going from Monterry to whatever the new machine has?
MacBook Pro (M2 Pro, 2023)
It is not necessary to upgrade first. You can simply transfer the content of your existing Mac to the new one by following Transfer to a new Mac with Migration Assistant - Apple Support.
Newer Macs do not back up or transfer macOS itself anyway, which obviates the concern you may have.
You can transfer content directly from one Mac to another or from its Time Machine backup — it makes literally no difference, assuming the TM backup is current.
How to migrate macbook on Monterry to new M2 macbook
