you might still be able to use the remove method of the UserMenuService to remove certain items from there.
As an alternative you could also add a stylesheet that would take care of hiding the default user menu entry.
The approach that you tried in Micro Front-end - Customize the left navigation menu (replacing the default implementation of a service with custom implementation of that service) will not work with micro frontends. You can how ever still use the API offered by these services to remove certain elements from their state if supported. How ever this is still not how micro frontends were meant to be used as they were meant to add functionality, not remove it.
Regards,
Tristan