New MacBook Pro - can't locate my LR Catalogs

By default Lr creates catalogs in the Picture folder. Unless you specified a different location, or moved your catalog, that’s where you will find it. The pictures folder is found in the Username home folder. When Lightroom creates a catalog, it actually creates a folder by the same name. When moving a catalog to a new location, you need to move the entire folder, not just the .lrcat file.

If you need to locate your LR Catalog the easiest approach is to use Spotlight to search for files with an "LRCAT" extension. This will show the Lightroom catalogs you have generated and also the backups. These can be copied to your local harddrive and placed on your new Mac Book Pro,

Also, see if this link helps. It has a video tutorial from Adobe Evangelist – Julieanne Kost:

Move LR to a New Computer

Here you'll find infomations about moving LR to a new computer.

https://www.lightroomqueen.com/how-move-lightroom-to-new-computer/

In this article you'll find infos about location LR catalogs

https://www.lightroomqueen.com/merging-catalogs-1-identifying/

Moving from Downloading, Installing, Setting Up to Lightroom Classic CC — The desktop-focused app