Apple support team shares the Apple Support Guide for Users in this article for some common issues which given below

Back up iPhone using iCloud
Back up iPhone using your Mac
Back up iPhone using your Windows PC
Back up iPhone

You can back up iPhone using iCloud or your computer. To decide which method is best for you, see About backups for iOS devices.

How to back up your iphone

Back up iPhone using iCloud

Go to Settings > [your name] > iCloud > iCloud Backup.
Turn on iCloud Backup. iCloud automatically backs up your iPhone daily when the iPhone is connected to power, locked, and on Wi-Fi.
To perform a manual backup, tap Back Up Now.
To view your iCloud backups, go to Settings > [your name] > iCloud > Manage Storage > Backups. To delete a backup, choose a backup from the list, then tap Delete Backup.

Back up iPhone using your Mac

Connect the iPhone and your computer using USB.
In the Finder sidebar on your Mac, select your iPhone.
Note: To use the Finder to back up iPhone, macOS Catalina is required. With earlier versions of macOS, use iTunes to back up the iPhone.
At the top of the Finder window, click General.
Select “Back up all of the data on your iPhone to this Mac.”
To encrypt your backup data and protect it with a password, select “Encrypt local backup.”
Click Back Up Now.
Back up iPhone using your Windows PC

Connect the iPhone and your computer using USB.
In the iTunes app on your PC, click the iPhone button near the top left of the iTunes window.
Click Summary.
Click Back Up Now (below Backups).
To encrypt your backups, select “Encrypt local backup,” type a password, then click Set Password.
To see the backups stored on your computer, choose Edit > Preferences, then click Devices. Encrypted backups have a lock icon in the list of backups.

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