Hi Hi. I have exactly the same situation. I spent ages talking to "support" (lol) who kept asking what browser i was using, whether i was using the app (no). Telling me to clear cookies, cache etc. These support have NO IDEA about the web programming. Someone has obviously tried to change it to a drop down "menu" and then have not made it a drop down that works.
Try looking up you own listing without being logged on, click on it and then try logging in.
This may enable you to access the calendar page. Or hit the top left AIRBNB logo and send a message from the master page...ie who's arriving today and in the next few days.
Transaction history has also disappeared, also listing, inbox etc.
It's not your fault. Hope that helps. 🙂 Andy