Get an external hard drive or NAS (Synology makes well-supported devices), go to takeout.google.com, request an archive of your photos, wait a couple days, and

Get an external hard drive or NAS (Synology makes well-supported devices), go to takeout.google.com, request an archive of your photos, wait a couple days, and then download the archive. Note that the takeout archive will most likely not contain your original images. Google photos deletes, and in some cases rewrites, the metadata in your files. It's much better to back up your photos and videos directly from your devices. I use Resilio Sync or SyncThing to do this automatically, and then use PhotoStructure to manage and view my photo and video library on my own hardware.