Update one week later.
Still no response from Revolut. My luck is that my wife and I co-shared the same account and she managed to log in on her new phone. We have now withdrawn all available funds from our account.
It is all too easy to lose access to your account (SW bug in my case?), and it is extremely difficult to receive support and regain access if the app is not working. And if you lose or damage your phone, what then? Tough luck! What a horrible experience.
For these reasons I do not recommend anyone to open an account until there is at least a phone support number and a web interface available.
Needless to say, I will not even bother to try and get in contact to close my account. I will happily just move on and forget this little bank experiment ever existed.
Sincere wishes and good luck to the rest of you in this thread.