https://macresearch.org/this-password-has-appeared-in-a-data-leak/
"If you have checked your iPhone or iPad’s passwords menu and you have found a warning telling you “This password has appeared in a data leak, which puts this account at high risk of compromise. You should change your password immediately”
"What this message basically indicates is that the password you are using for your account has been made publicly available on the webspace.
Why you are getting such a message in the first place?
Unfortunately, in this digital era, no one is fully protected against data leaks. Big and small businesses and their websites and servers are hacked all the time by active cybercriminals and people with malicious intentions. Known data leaks are typically stored in public databases that are available online. These databases allow you to manually search them for your passwords, see which websites have suffered data leaks, and even receive personal alerts about credential leaks related to your accounts.
But how does Apple know that your passwords have appeared in a data leak? Well, this is a new feature built into iOS 14 called “Security Recommendations” that monitors your passwords and notifies you if they show up in known data leaks.
"When turned on, the service checks if any of the sites you have accounts on has been pwned, then checks the last date you updated your password. If the date of your last password update is older than the date when the site was pwned, then you’ll see a warning on your Apple device.
The new “Security Recommendations” feature does that monitoring automatically and matches your stored passwords against known databases with leaked passwords. If there’s a match, you’ll be alarmed by a “This password has appeared in a data leak,…” message."
Think thats clear enough. A site (This one) that does not take its security seriously, fobs off its users and openly sanctions defamation of its users is not one I wish to be associated with.