I just had a very annoying interaction with the tailscale Android app:

It wanted me to log in for some reason even though it had worked fine for months. Login uses my Google log in.

When I try that, Google asks me for a hardware key to complete the login, even though it's my phone and I'm already logged in.

Eventually I figured out that if you select "log in using another device" and then click cancel when it brings up the qr code, you can select a push notification on "another device", which actually pops up on the same device. Do that once and it fails. Do it a second time and it succeeds.

All to use the tailscale app on my own phone.