So if you already have an existing photo library, does that mean an existing library in Lightroom? Or something else?
Sadly, no it is not a photo library, it is a Photo(successor to iPhoto) library residing in the Pictures folder on the computer hard drive.
You mean to say Apple Photos ( S at the end).
You need to copy, maybe move, the Masters folder from the Photos Library.library package folder to some other folder on your hard drive. Then you can import them into LR.
None of the edits you did in Apple Photos will be included but at least you will have your images in a program that doesn't want to take total control of them.
To get to that masters folder you will need to Right Click on that library package and select Show Package Contents. It will then expand into some other folders one being the Masters folder. Just copy/move it to another folder you create on your drive.
Thanks for helping.Big decision as there are over 30,000 edited photos!