Managing Photos system file

I'm running Monterey 12.7.6 on a MBPro 15-inch, Mid 2015 Intel machine. Some time ago I moved the system photos file to an external drive to conserve space on the laptop. I can't remember the steps I went through to do that, what the filename has to be, etc. I have a new MBPro 16" M4pro. How do I get the photos file from the external drive to the new machine? My 2015 machine only has 13GB free...the photos file is 51GB. Where can I find documentation for doing this? Going forward, is it better to just leave the photos system file on my laptop and not try to work with it on an external storage device? Importing photos from my iPhone should be simple but it doesn't seem to be. The whole photos arena is very confusing to me. Maybe it's simpler on Sequoia. Thanks to anyone who can help me!