Hello AlexPamov,
Thanks for connecting with Apple Support Communities.
We understand that you backup to iCloud on a weekly basis. However, your photos appear to not be syncing as expected. To clarify, do you have iCloud Photos enabled? If so, having enough space is very important. When you exceed your iCloud storage limit, photos and videos won't upload to iCloud and your library won’t stay up to date across your devices. Thanks for ruling that out as an issue.
We'd like to provide you with a few steps that may help resolve the issue:
• Update your iPhone: Always be sure that your device is running the latest software version. This is to ensure that everything runs smoothly. It can also resolve any software related issues that you may be having.
• If you're using any other iCloud features such as Mail, Contacts or Messages, verify that they are working as expected. If you're experiencing an issue with other services, this could indicate something else may be causing the issue.
• Make sure that you are using the supported file types:
"What file types upload to iCloud
iCloud Photos and My Photo Stream upload your collection to iCloud each time your device connects to the Internet and your battery is charged. iCloud will upload these file types.
- GIF
- JPEG
- HEIF
- HEVC
- MP4
- PNG
- RAW**
- TIFF"
More details here: About iCloud Photos and My Photo Stream
• Verify if there an issue with the sync status. "When you turn on iCloud Photos, the time it takes for your photos and videos to upload to iCloud depends on the size of your collection and your internet speed. If you have a large collection of photos and videos, your upload might take more time than usual. You can see the status and pause the upload for one day.
- On your iPhone, iPad, or iPod touch, open the Photos app, go to the Library tab, and tap All Photos. Then scroll to the bottom of your screen."
Click here for more info: Set up and use iCloud Photos
If you continue to experience the same behavior, we suggest that you reach out to Apple directly. You can follow this link to connect with them: Get Support
Take care.