Digitalstrom implementation

all that I need is a smart system for the front door of the house and the doors for each individual flat.
I want to integrate into my HA (what is for my flat only), I don’t think that the other residents that much in home automation.
One flat using smart lights and sockets but as far as I know they use a proprietary system but don’t know the details yet.

I will us another system for other devices in my flat.

The installation has to be done by an qualified person as I don’t want to be responsible for the proper function of the front-door bell system (I don’t have the time to do so and insurance is anther topic to regard).

dS just told me that they don’t have their own system, the would use e.g. DoorBird, so even better, as it allows to use other vendors.
Unfortunately, DB is not that easy to install Doorbird, is it any good?