Is there any way to check if someone stole my data through my network?

If you have unauthorized apps loaded, you already have a catastrophic breach of security.

If you have apps with questionable security or questionable privacy practices or implementations, remove them.

As for the bulk of this question, detecting these breaches involves learning more about security and security reviews, and reverse-engineering apps and app communications. Sometimes about being sneaky; depending on context, adding a canary trap or otherwise. Specifically determining whether a breach has occurred—outside of catastrophic security breaches—can be a technically-challenging process.

Ransomware, blackmail, "defacing" attacks, reset passwords, finding sensitive data outside of your control, and other such, all serve as evidence of a breach.

For recommendations on security and privacy practices and settings from the folks at Apple, see:

... https://help.apple.com/pdf/personal-safety/en_US/personal-safety-user-guide.pdf

If you're looking for a cheap and easy way to detect iPhone breaches, that tends to be the province of snake-oil solutions and sketchy "security" apps.

There have been scanners implemented for specific security breaches, but those are also typically targeted breaches and used against dissidents, activists, investigative journalists, and those with access to sensitive or classified or similar data—and if you're potentially among those of interest to an entity with vast resources and wealth, you really need specific and tailored assistance with your own security.

Here's a non-partisan description of security for folks that can be targeted: https://democrats.org/security/

Mohelbaz11 wrote:

dear mr @hoffman thanks for help but I’m asking about my mac not iphone

The answer remains the same—absent direct or overt evidence of a breach, you’re headed for reverse-engineering and network-monitoring, and that is difficult and detailed and very far from certain to find compromises.

See the previously-linked information, and particularly for how to improve your own security. Too many of the breaches are against us, and not against flaws in our devices and computers. We get phished, or scammed, or confused, or frustrated, and expose our credentials, or we get convinced to install problematic apps, and we get breached.

These ”am I hacked?” questions are the foundation of an entire industry of too-often-sketchy add-on “security” products and too many of which are ineffective, privacy-invasive, incorrect, or themselves vulnerable to exploitation, and these add-ons are too often used as a means to cause inexperienced and unwary users to install actual malware onto their devices and computers, too.