Displaying errors on frontend user forms I'm trying to get some feedback for the user on registration when the username already exists but I don't know in which object the errors are.

I use the form they provide in the docs:
https://docs.craftcms.com/v3/dev/examples/user-registration-form.html

Same for the forgot password form if the user doesn't exists in the system, I'm not able the provide the right feedback with this form:
https://docs.craftcms.com/v3/dev/examples/forgot-password-form.html
I just tested this with the user registration for in your link and got the expected behavior when you try to register with a username that already exists.



A few things to check.


Make sure you have public registration enabled in the Control Panel under Settings->Users->Settings.
When you're testing registering a user in your front-end form, make sure you're logged out of your current user account.