if someone tries to access i you stop it

No one can access your iPhone without your consent.

If you feel an unauthorized person/app is remotely accessing, controlling, or monitoring your device, then that is possible only if you have done one or more of the following Don'ts...

1. Don't hand over an iPhone to kids or to a stranger without Enabling Guided Access
2. Don't share Apple IDs
3. Don't Jailbreak
4. Don't share sensitive information pertaining to your device
5. Don't give in to Phishing
6. Don't plug in your device in Airports and Public places through third-party cables and trust the device. Beware of Juice Jacking. (Especially in India)
7. Don't leave your iPhone unlocked and unattended in public places like offices, schools, malls, etc.

If one of the above is true then quickly change the Apple ID Password and Return iPhone settings to their defaults.

If you have activated Face ID on your iPhone 13 Pro Max, then everyone who needs to access your iPhone must use your face recognition to enter, or your passcode.

Other people cannot sign in to your iPhone with Face ID. They will be asked for the passcode, and if they don't know it, then there is no access.

You can see how to set up Face ID here:

Use Face ID on your iPhone or iPad Pro - Apple Support

If you suspect that someone knows your Passcode, see how to change it here:

Use a passcode with your iPhone, iPad, or iPod touch - Apple Support