Good afternoon alexanh9999,
Welcome to the Apple Support Communities!
It sounds like you recently updated your iCloud Storage, and are having issues with photos and videos uploading to iCloud.
Are you saying that you had 21,000 photos and 700 videos stored on your iPhone 12 Pro, and you have just enabled iCloud Photos? What is the capacity of your iPhone 12 Pro, and how much space is available on it?
How to check the storage on your iPhone, iPad, and iPod touch
If you enabled iCloud Photos, then your photos will no longer be included in an iCloud Backup of your iPhone, as they are already in iCloud. Review this information carefully:
Set up and use iCloud Photos
iCloud is a syncing service. The photos or videos you add, organize, edit, or delete on one device will be synchronized on all devices signed in with the same Apple ID.
How long it takes for your photos and videos to upload to iCloud Storage depends on the speed of your internet connection. Use a Wi-Fi network for this, not your cellular data.
"To see the status of your uploads, open the Photos app, open the Library tab, and tap All Photos. Then scroll to the bottom of your screen."
Do you have a Mac or Windows computer? If you have a Mac with iCloud Photos enabled, you can export files (such as your videos) to an external drive to free up iCloud Storage.
Export photos, videos and slide shows from Photos on Mac - Photos Users Guide
Take care.