If you want to access your icloud information from a third party app you need to use an app specific password this helps protect your account by allowing you to sign in securely learn how to create and use app specific passwords if you still need help.

Manage the apps that can sync with icloud a list of icloud compatible apps on your mac appear in the right panel to prevent an app from syncing with icloud in the future remove the checkmark from the apps corresponding box.

If youre signed into icloud and have a passcode enabled youll be prompted to enter the passcode for your device follow the onscreen steps to update your password on your mac with macos catalina or later choose apple menu system preferences then click apple id.