Importing catalog issues Mac Mini M2 Pro

I installed Lightroom Classic to the new Mac Mini. 

Was that a proper fresh install?

Did you install the Adobe Creative Cloud Desktop App, then use that to install your various Adobe apps, including LrC?

Or did you use Apple Time Machine (copy) and copy onto the new MAC? A very Apple centric approach that fails.

I Made a copy of the Lightroom folder found in the IMac. There were a lot of items there, so I made a copy of the v12 items including the .lrcat and copied them to the Mac Mini. (The Pictures folder)

Was that the folder your catalog was in? Or where the program was in? The lot of items statement makes me wonder.

When I double click the .lrcat Lightroom is starting but after a few moments I get an nearly empty screen with a exlamation mark in a triangle. 

One test or diagnostic step to attempt. This to rule out (perhaps) the catalog. Instead of starting LrC in any manner that would open an existing catalog, do so in a way to create a new catalog. One way to do this is to hold down on your Option key (ALT on Windows I think), while double clicking on the LrC shortcut icon. Then in the dialog you get, select New Catalog.