Hello Yenthe.

First of all, thanks for your detailed answer. In order to try your suggestions out I created 2 fictional users (Marie Curie and Isaac Newton)

My results:

• Under Settings > Users & companies > Users. I left all Application Accesses in blank ( I don’t want them to see any original Odoo app) Despite that configuration, both users are able to see almost all apps that are installed on the branch. “Apps” and “Settings” went away though.
• My custom apps -made using Studio. are named "Capacitacion" and "Dots". In order to apply what you said I tried to create a group for those apps, but they were never found. I was unable to fill The field “Application”

• Why is it that both users can still see almost all installed apps and I am not able to find my custom apps on the Group configuration view? Am I still doing something wrong?

ps: I had some screenshot to show better the result I was getting but the reply never went through with the images

I try answer with my experiences in Community Edition (C.E) Version of odoo,,

In Odoo C.E,,  the menu can be accessed/visible by active user if:
- The group of user granted in menu (Settings->Technical->User Interface->Menu Item ->Access Right (Groups))
- Active user has granted by Access Rights (ir.model.access) to accessing the model object

So in my opinion,, why after you leave blank all user application access in User menu but still user can access the menu its caused by the user has granted on access right or menu access right.. You should check access right menu and check the granted user group on the model.

On odoo Enterprise Edition as a far i know the group rules and access right system/flow was similiar with at odoo Community Version

Regards.