iCloud storage is full.
Why is my iCloud storage full even after deleting 300 photos and videos from my phone? Yes, I also removed them from my recently deleted items and also restarted my phone after.
iPhone 8 Plus, iOS 15
See the following Apple articles:
How to use iCloud on iPhone
How to use iCloud on iPhone – Apple Support (UK)
Sign in and use iCloud.com
Sign in and use iCloud.com – Apple Support (UK)
Check your iCloud storage online or on any device
Check your iCloud storage online or on any device – Apple Support (UK)
Manage your iCloud storage
Manage your iCloud storage - Apple Support