How to add a checkbox to registration and user profile?

I need to add a privacy policy checkbox to user registration AND user profile (checkable and uncheckable at anytime in your user life). I was thinking there would be tons of plugins doing this, but I am searching for hours not finding anything suitable.

I could find how to add a checkbox programmatically to registration form (like this) but not on the user profile. So how this can be done?

To add fields on user profile page,there are some filters for displaying them and some filters for saving them and another action for updating personal options.