Sorry, for now only the Android version of Keychat supports Amber login.
As NIP-46 is not stable enough, we don't yet support the NIP-46 remote signer.
I can't log in to AQSTR using keychat if I log in to Android Keychat with Amber.
If I create a new npub/nsec directly in keychat, I can log in to AQSTR.