I mentioned it in a different comment, but take a look at Syncthing. It does mesh-style backup to synchronize a folder between multiple machines. That provides robustness against hard drive or PC failures, and it's easy to add an offsite node for extra confidence.

You can use Takeout to bulk-download photos: https://support.google.com/accounts/answer/9666875?hl=en

I don't know if you can automate syncing Google Photos to a local disk. Wouldn't be surprised if there was.

(edit: Wow. Lots of people wanting to help! I wasn't expecting two sibling responses.)

Yeah, https://github.com/gilesknap/gphotos-sync.

There's a decent guide here: https://ubuntu.com/blog/safely-backup-google-photos.

I run this every night on a raspberry pi, syncing them to my local NAS which is in turn backed up to cloud storage.

https://takeout.google.com/ is exactly what you want. Deselect all, check "Google Photos", click Next, chose your archive format, confirm. It'll take some time but at the end of the process, you got a nice zip with all your Photos in original quality.

I found a solution: Use Photos (iCloud photos) along with Google Photos since I already use an iPhone. Thanks for the comments, but I believe this is the easiest.

I suggest migrating to Nextcloud and then following the 3:2:1 methodology for preserving data - 3 copies 2 local 1 remote (encrypted offsite)