Earlier quoted context omitted.
That’s not true. On any Mac or iPhone you can choose the iCloud Photo Library storage option to download all instead of letting the system optimize the storage. And if you turn off iCloud Photo Library, it will also try to download it all. I know this because I stopped using iCloud Photo Library and that was how I got all my photos downloaded.
+1 to this method. After optimise storage is disabled on the Mac, wait for all photos to download. Then, open the photos library bundle and you'll see every photo there, full res. Copy them wherever you like. Also, if you leave optimise storage disabled and continue to use Photos, every photo will be cloned in any local or cloud backups of your machine. This strategy creates additional photo redundancy separate from…
Not sure if the open/close is required, but I didn’t want to find out.