Transferring Catalina system drive to older Mac — possible? I have have been running Catalina on my long-in-the-tooth Mid-2012 13" MBP. As I'm now getting a new work MBP, I wanted to give my wife this MBP, and take hers (pre-2012, and therefore can't install Mojave or Catalina in its current state). However... I still need a machine to do occasional freelance work on... so I was wondering, could I install my system HD in my wife's older MBP, and have it "just work"? Like, would it successfully boot into Catalina? Or would it balk at the older hardware on boot? Or some other kind of non-/semi-functioning? (I'd like a canonical answer, but personal experiences are also really helpful.)
In the past, you could quite simply move a boot drive from one Mac to another &amp; have it work as though nothing had changed. The only proviso was that both machines were of an age to know what each OS is, not too new, not too old.
I've been doing this with Macs for decades. 

If the 'jump' between OSes would have required a firmware update, that may be a stumbling block, however, if the Mac you want to transfer the drive to cannot run the OS on the drive, then this simply will not work at all.