Salutations GrumpyOldMan45,
Thank you for taking the time to visit the Apple Support Communities! It seems you have an inquiry regarding the strong passwords feature for iOS. We will be honored to assist you!
“ Passwords are generated based on heuristics that determine whether a password-field experience is for password creation. If the heuristic fails to recognize a context-specific password being used at password creation, app developers can set UITextContentType.newPassword on their text field and web developers can set autocomplete= “new-password” on their <input> elements.
To help ensure that generated passwords are compatible with the relevant services, apps and websites can provide rules. Developers provide these rules using UITextInputPasswordRules or the password rules attribute on their input elements. Devices then generate the strongest password they can that fulfills these rules. ”
Please see the articles below:
Automatic strong passwords
Automatically fill in strong passwords on iPhone
Have a joyful day!