How can I tell if my iPhone has been hacked?

Why in the world do you think that means your phone has been hacked? You simply posted a line in the analytic logs that are part of the FedStatsMLHostPlugin process. It is an Extension in your System library that is locked on your iPhone, that no one can even access to install any files.

Yes, your phone is supposed to have that process and part of iOS 18. Do yourself a favor and stay out of the Analytic logs. You have no way to decode what they even, and just like this one, it will leave you making outrageous claims.

https://newosxbook.com/ent.php?osVer=iOS18&exec=FedStatsMLHostPlugin

A normal user like me does not want to know what these analytics/diagnostic data mean.

These are meant for diagnosis when the iPhone goes for service or repair at the Apple Authorised Service Center.

Check for Conflicting Apps: If the issue started recently after installing a new app, try uninstalling it and see if the problem persists.

While I wouldn't personally act on the Analytics report you provided, I encourage you to explore it for potential improvements. Taking this step is unlikely to have negative consequences and may boost your confidence. --> General Troubleshooting iPhone Issues: St… - Apple Community

This may help you --> Share analytics, diagnostics, and usage information with Apple

If you are experiencing some serious issue in the function of the iPhone then...

Take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support:

Apple Repair and Repair Status Check - Official Apple Support

Apple Authorized Service Provider

Find Locations - Location Selector - Apple

Contact Apple for support and service - Apple Support 

Alternatively, you may ...

Get a Genius Bar Reservation and Apple Support Options - Apple

Contact Genius Bar.

Manage Reservations - My Reservations - Apple

Keep the iPhone updated to the latest iOS always and never Jailbreak. That's it.

iOS / iPadOS devices cannot be hacked or infected with Viruses / Malware / Spyware *** unless you have intentionally downloaded spurious software or unauthorized apps directly from the internet and installed them on your device, and/or have Jailbroken. 

It (Hacking) also depends on how careful you are in sharing sensitive and valuable information pertaining to your iPhone such as Passcode, Password, etc with your friends and family members.

Be judicious when sharing the device's sensitive and valuable information with friends and family members.

**The primary reason for this is Sandboxing. All third-party apps are “sandboxed”, so they are restricted from accessing files stored by other apps or from making changes to the device. Sandboxing is designed to prevent apps from gathering or modifying information stored by other apps.

Security of runtime process in iOS and iPadOS - Apple Support

The sandbox on an iPhone is a security feature that creates a restricted environment for each app to run in isolation from other apps and the operating system. It is a core component of iOS's security architecture and plays a crucial role in making iPhones more secure.

If you doubt the authenticity of the information provided earlier, you have two alternatives:

1. Report the hacking incident to local law enforcement authorities and actively pursue the case.
2. Accept the credibility of the information; it is impervious to hacking. Just as some individuals hold unconventional beliefs, such as a flat Earth or moon landing denial, one has the freedom to believe in anything. The choice ultimately rests with you in this open and free world.

Your phone has not been hacked.

Analytics is completely useless unless you have the special software to read the code and special training to know how to interpret the results.

Do you?