Found my own answer:

ALL Outlook 2019 data on the Mac is kept in the following folder:
~/Library/Gourp Containers/UBF8T346G9.Office/Outlook

Renamed above folder to Outlook0 (could have deleted it but just in case!)
Copied ~/Library/Gourp Containers/UBF8T346G9.Office/Outlook folder from old drive
Pasted it to same path on new system.

The only thing I had to do was to enter the passwords for each one of my mail accounts under Outlook > Tools > Accounts.

Hope this helps some other poor soul; I had just about given up on my OL data!