It sounds like your phone might not be compatible with the Airbnb app currently - you can find the the latest requirements for it to run on👉this page. Are you able to update your device to that version, or do you have access to another device perhaps?
In the meantime, you can keep accessing the platform via any browser.
As explained in the post, the problem is that Airbnb did not provide for backward compatibility in your app. Airbnb could have done this and it is possible to make your app backward compatible. The VRBO app works just fine on my current iPhone. It just depends on how much you value your customers.