Your best bet is to copy and or move all your images from the Photos folder they were stored in to some other folder that you create.
To do that you have to expand the Photos library package folder and find the Masters folder. Do a Google search to find this package folder and how to extract your images from it.
In Photos, select all the photos that you want to put in LR; select "Export" from the file menu and export to a new folder on your hard drive. Finally in Lightroom, import the photos in this new folder.
Doing what is suggested above will get all your images to a new folder on your hard drive and it will preserve any edits you did on them. But if you are shooting RAW those RAW images are still locked up inside the Photos library package folder and what you will get is just JPGs of them.
If that is OK with you or you are shooting just JPG images, No RAW capture, then go for it.
Have got it
The RAW files can be exported as the Unmodified Original Raw files as shown below.
But if you do that you end up with 2 copies of the RAW files, one that you exported and one in the Photos Library Package folder, and how do you know Photos hasn't modified them in any way.
Instead of using Photos it is easier and better to just copy or move the original files from the package folder then Delete the one in the package folder if you copied them.
Then of course never open the Photos app again.