How to safely restore iCloud data on a compromised iPhone?

Tilavenil wrote:

How can I safely restore data from iCloud if my iPhone has been compromised?

A family friend has the iPhone 13 running an older version of iOS. I dont know what version exactly, but owing to space constraints, they have been putting off the update for a while now.

We suspect the device has been compromised somehow with a third party gaining access to WhatsApp and Instagram chats. It would appear the third party is receiving keystrokes and/or images (screenshots) from time to time, as they sometimes allude to certain parts of chat messages that were private.

We added a PIN to WhatsApp and 2FA to Instagram, but still have not been able to stop this menace.

We are considering resetting the current device (getting a new device is also being considered) but would very much like to know how we can safely restore data from iCloud without the menace of any malware ending up on the device again.

Please advise!

[Re-Titled by Moderator]

Original Title: Whatsapp and Instagram hacked

Has your friend changed the password to both apps?

The iphone itself doesn't contain malware, nor the backup.