I put lightroom on my new Mac and I cannot imports any pictures that are in my photos application. It looks as though it only sees my old Mac as a source to import from.
Photos stores your images in a buried folder called Masters. that folder is hidden inside a Package folder that ends with .photoslibrary.
Photos Library.photoslibrary in the Pictures folder
You have to right click on that package folder and select "Show Package Contents" then it expands to many different folders.
Lightroom can't see that Masters folder because it is hidden by Apple, Mac, OS X.
So you need to Copy that Masters folder over to some other folder on your drive. Like to the Pictures folder.