How can electrical outlets be sealed airtight?

Hi

We had a condominium thoroughly renovated. After moving in, it turned out that one room (children's room) developed strange odors. It smells like a kitchen or sometimes musty.
Context:
- 3rd floor apartment building
- on the ground floor there is a pizza service

A neighbor has a similar problem and wrote the following but received no response:

"As you may recall, after such a long time, the district office no longer considered itself responsible for investigating the matter with the unsealed cable ducts below in the pizza taxi and referred it to the property management.
This sealing was omitted back then (around 2005/2006) because the suspended ceiling as well as a ventilation unit were already installed.
During a previous inspection by the responsible chimney sweep, this fact was confirmed by measurements.
We notice this daily through the more or less strong odor nuisance in our living spaces.
Furthermore, there is certainly a danger that in the event of a fire, toxic (deadly) smoke gases can enter the apartments from the 1st to 3rd floors (possibly also 4th floor right) into the apartment."

Additionally, I also believe that odors from our own kitchen pass through the exhaust hood via the socket and cable duct into the children's room.

Questions:
How should I proceed? How can sockets be sealed airtight? What kind of craftsmen are suitable here? How can I have our apartment adequately sealed? How should I approach this best and cost-effectively?

How do I proceed? How can electrical outlets be sealed airtight? What type of craftsmen are suitable here? How can I have our apartment sufficiently sealed? What is the best and also cost-effective way to approach this?

Maybe first check whether and how "shafts" and "cables" could be the cause at all. What kind of house is it? Older or new? Solid construction or timber frame? Where do the cable shafts run? In classic, somewhat older solid construction, no empty conduits were usually installed for cables; instead, they were simply laid in the wall and plastered over. You can try removing an outlet and check (Note: turn off the fuse). This is how you proceed. Step by step.

Solid house multi-family house. circa 1980. Removing the socket is already a good step, thanks ;-)))

Solid multi-family house. Approx. 1980. Removing the socket is already a good step, thanks ;-)))

Given the year of construction, I assume it is NOT the socket, as it is very likely that no empty conduit was used.

I assume that with the year of manufacture it is NOT the socket, as most likely no empty conduit was used.

, then where can kitchen smells come from? All other rooms are not affected. The window is also very tight (second highest sound insulation).

where can kitchen smells come from then?

No idea. Maybe from the materials used during the renovation.