Is it the standard notification you get from iPhone?
If you find out a password has been compromised, don't panic! It doesn't mean a hacker has gained access to your account. It simply means Apple has found your information in a data breach, and you should change your password immediately. Security recommendations will be listed in order of priority
How to view compromised passwords
iCloud keychain typically notifies you about potential data breaches through push notifications if you have them enabled on your iPhone or your iPad. If you don’t have push notifications enabled, you can still view the information on the Security Recommendations page in settings. Here’s how to find it:
Open Settings on your iPhone.
Scroll down and tap Passwords.
Choose Security Recommendations.
You’ll either see a list of things to fix or no issues found on this page. If you find out a password has been compromised, don’t panic! It doesn’t mean a hacker has gained access to your account. It simply means Apple has found your information in a data breach, and you should change your password immediately.
Security recommendations will be listed in order of priority. At the top will be passwords that have been exposed, and at the bottom will be passwords iPhone views as weak or ones that have been reused, and you should consider strengthening.
you can check here for breeches
haveibeenpwned.com/