Is my iPhone XS compromised ?

You will want to ask the investigator to elaborate on their comments. They could well be an expert in digital forensics and security, and well versed in recovery. Or, well, they could conceivably be just blowing smoke. We don’t know them, nor do we know the situation here, nor do we know why the investigator told you what they did.

Malware is rare, and is targeted based on available information.

It is possible to cause problems with an Apple ID compromise. An Apple,ID compromise is more likely than an exploit, as well. Review the following guide, and run Safety Check.

Personal Safety User Guide - Apple Support

That’s improbable. Did you jailbreak your device? If not, your device is not compromised.