Hey there, I get your concern.
I think you should register asap here in
Mieterverband and ask the directly what a renter can do in your situation. I am sure they will be able to help you, this scenario is not uncommon.
Well, now, personally, I wouldn't move in for a month and have the apartment aired, even if I had to pay the rent for this time and hotel. You may be compensated for your hotel.
Formaldehyde is really bad, I am not sure how much people care for that here, though. When we had stuff painted in our bathroom, I took the kiddo and left for 2 weeks so we would avoid inhaling it. But, a few weeks ago, downstairs neighbors decided to re-parkette the whole place and all the fumes went directly through holes into our place. I was livid but there is not much one can do, just leave the windows open in the entire apt for days, it dries quickly.
It's not only parkettes that exude the toxins, but new carpets as well (it's the foamy layer on the bottom of the carpet) and generally most types of flooring. Depends on the material, some air quickly and that's it, some take months.