Was looking for a way to have unlimited original quality photos for iPhones with Google Photos.
Can install Syncthing app on Google Pixel and iPhone (or any other phone).
Link both the phones. Select folders to sync across.
Enable auto upload in Google Photos only on Google Pixel.
Make sure you have the same Google account on both phones, that way you can see the photos that are synced.
Enjoy unlimited original quality photos.
Credits to Baka Baka for sharing this trick.
This is a good way to avoid spending on subscription evey year just for photos.
Most of the apps requires Android 5+.
You'll be fine.