I need to upgrade my iMac and hope to move most of my data onto an external drive. I use Lightroom Classic as well as Photoshop and currently have around 16,000 photos in my Lightroom catalog so I don't want to have to reconnect them all! I would prefer to have the catalog itself on the new hard drive to get the best performance.
I have seen a couple of posts on this subject (with useful replies) from a few years ago but was wondering if there was anything different in the current advice.
Upgrading the iMac — by doing what? You don't really say what changes to the iMac are going to happen, and that you want to move the photos. I guess the answer really depends on what change to the iMac are planned.