Hi there,
iCloud Keychain stores passwords for various website and apps, as a change is made to those sources.
Set up iCloud Keychain - Apple Support
iCloud Keychain remembers things, so that you don't have to. It autofills your information—like your Safari and app usernames and passwords, passkeys, credit card information and security codes, and Wi-Fi passwords on any device that you approve.
So, when you make a change to those sources, iCloud Keychain is updated, such as for the apps you asked about.
This page has some info on iCloud Keychain, which also can help:
View your passwords and related information on iPhone - Apple Support
This page has some iPhone password info:
How to find saved passwords and passkeys on your iPhone - Apple Support
Take care!