Upgrade from iMac (27-inch, Late 2012) 24-inch Blue iMac
How do I move my software from the old iMac to the new 24-inch iMac?
iMac 27″, macOS 10.15
Using your Time Machine backup, is the fastest and easiest way to move from the 27" to the 24" iMac.
see > Move content to a new Mac - Apple Support
Migration moves your user setting and data into the new macOS and App's. There is a chance, that you may need to update, reinstall or even replace some older third party App's.