Hi,
In the employee form, there is an option to add the home address id and the employee has a user

In the Home address field that related to the contact module based on
this record you can see the portal user grant access to the contact
module

this related user can link with the res.user model and that connect with the partner details

So each user has a related partner if the user can relate with partner we can set up the portal access

we can set up the access here, and based on the set it comes in the user view, also we can set the user email and password

added the access and set up the credentials

We can log in with these credentials and see the portal set up

Hope it helps
Hello Sylwia,
You can use the Employee application for that.
Are they internal users? I don't understand.