Migrate from El Capitan (10.11) to Catalina (10.15) I have a mid-2009 13" MacBook Pro still working, running 10.11 El Capitan. I would like to move it to a newer 2015 13" MacBook Pro currently running Catalina 10.15.


Of course, making sure the new MacBook Pro has an equal or larger hard drive;
Taking into account the old mid-2009 cannot be updated beyond 10.11;
Not knowing if the newer 2015 MacBook Pro could run El Capitan.


My best option seems to be the following:

Using the Migration Assistant (working with OS X Snow Leopard v10.6.8 or later): make a TimeMachine backup of the mid-2009 MacBook Pro, connect the TM backup to the newer 2015 MacBook Pro, launch Migration Assistant (within the utilities folder) and select the Time Machine backup. I assume that 32-bit app will be quarantined, but everything else would work (i.e. Mail, preferences for all working apps, etc.). Would that work?

I don’t actually know if the newer 2015 MacBook Pro could run El Capitan. If it could, another option would be to clone the older MacBook Pro to the newer one and then slowly update through all version of macOS, all the way to Catalina.
I ended up not migrating the whole machine. Since Catalina supports only 64-bit apps, it makes more sense to re-install one by one. Since most of my files (data) are synced online, no need to move them over either: I can find them back using a cloud storage solution (iCloud, Dropbox, OneDrive or pCloud).

The most important thing I needed to migrate over though that was not synced online was my mail archive: multiple mailboxes sitting on the machine itself (i.e. not on any active account such as Exchange or Gmail). The solution for this turned out to be simple: 

1) El Capitan was cloned on an external harddrive
2) External HD was connected to the new machine running Catalina
3) On Catalina, within the Mail App > Import Mailboxes... > choose “Apple Mail” continue > navigate to the external HD and find user/library/mail
4) Import

To improve management of archived email, I’d recommend using a third-party software such as MailSteward or EagleFiler.