I’m having a problem with storage on my phone after I OS 15 installed how do I fix it
Having a problem with phone storage after installing the iOS 15 update how do I fix it
iPhone 12 Pro Max, iOS 15
The link in blue above your name on this page should help. the only way to get more space is to delete photos, messages, apps, etc. Be sure to save important photos and data to your computer or an external drive.
Check this link also...
What's the difference between device storage and iCloud storage? - Apple Support