I'm using Odoo 15 and in my development environment the user form is showing group settings as usual, but in production a list with all the user's groups is shown instead.
I've posted the same question on StackOverflow, for Odoo won't let me post images or links :( . The StackOverflow question ID is 76564992.
Link: questions/76564992/odoo-15-user-form-showing-list-of-groups-instead-of-group-settings