Thanks to @ReVo_007 for mentioning Resilio Sync on another thread; here is how to backup photos to Google Photos for free.
Android
1. You will need an old Android phone with Snapdragon to load a custom ROM.
2. Popular custom ROMs are PixelOS and Pixel Experience; check the website to see if your device is supported. Or go directly to XDA for your specific device. Deprecated ROMS without update should also still work.
3. A Custom ROM tricks Google into recognizing your Android device as a Google Pixel, allowing you to access the unlimited photo upload feature that is still available for some Pixel devices.
4. Load the Custom ROM of your choice and install Resilio Sync.
iOS
1. Install Resilio Sync on your iPhone
2. Follow the prompt and select the Camera Photos
3. You need to manually open the Resilio Sync app and wait for the auto transfer of photos and videos to your android device.
You can choose any folder from the Google Photos app from Android to auto backup to your Google Photos.
Android
1. You will need an old Android phone with Snapdragon to load a custom ROM.
2. Popular custom ROMs are PixelOS and Pixel Experience; check the website to see if your device is supported. Or go directly to XDA for your specific device. Deprecated ROMS without update should also still work.
3. A Custom ROM tricks Google into recognizing your Android device as a Google Pixel, allowing you to access the unlimited photo upload feature that is still available for some Pixel devices.
4. Load the Custom ROM of your choice and install Resilio Sync.
iOS
1. Install Resilio Sync on your iPhone
2. Follow the prompt and select the Camera Photos
3. You need to manually open the Resilio Sync app and wait for the auto transfer of photos and videos to your android device.
You can choose any folder from the Google Photos app from Android to auto backup to your Google Photos.