What makes you think this? You would be receiving all the official emails being sent to the other person and they would find it diffiult to do account management if they couldn't get access to the emails. The main way I can think of that this would be possible would be if they had set up the account first, then abandoned the email address and Gmail allows address re-use after a period of time. In that case the Apple Account isn't yours, it is theirs because they had it first.
The only other way would have been if you had created the Apple account and then the other party took control over it. This would require that they had access to your email account, your trusted devices (e.g. telephone), your account password, etc. A major compromised account. Read this document if you think your Apple ID has been compromised. --> If you think your Apple ID has been compromised - Apple Support
For iOS 15 or earlier, if you want to see if anyone else has access to your device or accounts, click here --> See who has access to your iPhone or iPad - Apple Support
For iOS 16 or later see how Safety Check on iPhone works to keep you safe. How Safety Check on iPhone works to keep you safe - Apple Support
Use the information in this document to check your Apple ID device list to find where you're signed in --> Check your Apple ID device list to find where you're signed in - Apple Support
Related materials:
Personal Safety User Guide
Personal Safety User Guide - Apple Support
> open the Table of Contents and review the articles
A document with general information about security and your Apple ID --> Security and your Apple ID - Apple Support
Contact Apple for help with Apple ID account security by clicking on this link --> Contact Apple for help with Apple ID account security - Apple Support "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues."