Missing plaster inside at ventilation pipes.

You only have exposed brickwork with concrete and usually only extra interior walls that do not lead outside. But concrete is, of course, also airtight.

Unfortunately, I cannot answer regarding [Fachwerk], maybe there is also an airtightness foil somewhere or, as you say, it is deliberately built open. Leaks only become a problem if they are small, because then you create high volume flows.

Exaggeratedly said, if it whistles like crazy, you won't have a problem. However, your energy costs will shoot towards infinity because your thermal envelope does not exist.