You could setup your own ventilation for cheap if you have a window. But from a legal perspective the owner is supposed to do it: to my knowledge in the norms no shower is allowed unless you have ventilation. Depending on your existing relationships with the owners and how conflictual you’d like it to be, it may be as simple as asking politely… or you may take information from a tenant’s union and threaten with lawsuits.

EDIT: Yes humidity is a big problem for mold, and breathing problems!