I think there’s someone trying to monitor my iPhone remotely

Your iPhone cannot be hacked and controlled remotely from another device.

You can check if some devices you don't know are signed in to your Apple ID here:

Settings → Apple ID → scroll to the bottom. If there are one or more devices you don't recognize, delete them.

You must then change your password to your Apple ID, see here how:

Change your Apple ID password - Apple Support

See also this article:

If you think your Apple ID has been compromised - Apple Support

If you suspect that your iPhone has been hacked or someone is remotely monitoring you, there are a few steps you can take to protect yourself:

1. Change your passwords: Change the passwords for all your accounts associated with the iPhone, including your iCloud account, email accounts, social media accounts, and any other accounts you access on your iPhone.
2. Turn off network connections: Turn off Wi-Fi and Bluetooth on your iPhone to prevent any remote access to your device.
3. Restart your iPhone: Restarting your iPhone can help to clear any active connections and processes running in the background.
4. Update your iPhone software: Make sure your iPhone is running the latest software version to ensure any security vulnerabilities are patched.
5. Check for suspicious apps: Check your iPhone for any suspicious apps that you do not remember downloading. Delete any apps that you do not recognize or trust.
6. Consider resetting your iPhone: If you believe that your iPhone has been compromised and you are unable to resolve the issue, you may want to consider resetting your iPhone to its factory settings to ensure all data and settings are erased.

If you continue to have concerns, you may want to contact Apple support or a cybersecurity professional for further assistance.

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iOS 16 in iPhone 6s