I projected dividing the current garage space into two sections.
One section would grant access to the upper apartments via stairs and a lift, necessitating the construction of a dividing wall to allocate space for the lift and stairs.
The other section would include the room at the back, connected by a corridor from the shutter to the room and leading to the staircase accessing the basement.
This approach effectively creates a real estate unit composed of a room and a designated surface area, catering to your outlined needs.
Based on some published examples, I included 3D views so that you can have a clearer view of the project, these views will also include the waiting area and the reception (taken as a concept from the views published by you).

I hope you like this project, created according to the rules of interior design. Hoping to have met your requirements and provided useful ideas for the project, I greet you warmly.