Adding a custom input box at registration

[LEVI HAVIV]

Hello everyone,
I want to add a custom input box on the registration page, and for the data to go into mongodb about the user, for example, when registering they will need to enter the user's country, or anything else.
I owe it urgently, I've done dozens of searches on the forum, including this one
https://community.nodebb.org/topic/7979/custom-registration-form/8

And nothing works for me, I would appreciate clear guidance on the subject.
I tried to create a new extension even with GPT and absolutely nothing works.
Thanks for the help in advance!