Hi browndairycow :-)
Wondering if you have enough memory / storage free on your iPhone, for the operating system to operate smoothly.
Apple support have articles online (links below) that may help check.
How to check the storage on your iPhone
https://support.apple.com/en-us/HT201656
If storage space is a problem::
One way to free up space, is to transfer some of your important, or larger files (Photos, Videos, Music etc) to an external storage device. Eg: back up files to a computer, flash drive, or portable, external drive.
It seems iCloud storage is mainly used for syncing files across various devices, but is also an option.(A back-up is still important.)
What's the difference between device storage and iCloud storage?
https://support.apple.com/en-au/HT206504
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Ways to store or back-up photos and other files
Transfer photos and videos from your iPhone (ie to iCloud, Mac, or PC),
https://support.apple.com/en-us/HT201302
Or
Connect external storage devices to iPhone:
Eg: Attach the USB drive or SD card reader to the charging port on your iPhone using a compatible connector
https://support.apple.com/en-au/guide/iphone/iph95baac91f/14.0/ios/14.0
or
What is iCloud Storage:
https://support.apple.com/en-au/guide/icloud/mm7983cbca2a/1.0/icloud/1.0
And
Archive or make copies of the information you store in iCloud:
https://support.apple.com/en-us/HT204055
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And, if storage is not the issue:
If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open
https://support.apple.com/en-us/HT201398
If your screen is black or frozen
https://support.apple.com/en-us/HT201412
iPhone Battery and Performance
https://support.apple.com/en-us/HT208387
Hope this helps :-)
