For LR Classic, I just drag the photos I need in a "Import" folder in iCloud Drive and import. It's duplicated, but I can easily delete and recopy the originals in there if I need the space. The only bad thing about this is that it uses the "edited" photos and not the originals if you've edited them.
The other way, is to download the entire library in Photos, then import the whole shebang from the folder where Photos stores the files. It's a little excessive if you have a massive 800gb library like me haha. But I believe those pick up the original images without any edits in Photos.