Android App no connect

Hi, i have upgrade to 20.
But historically, we have not been able to access Nextcloud through the app.
i tried with the QR Code, it displays the url but it writes connection test and nothing.

Do you have an idea?

Without providing further information, it is unlikely to get an answer. What versions exactly are you using (Nextcloud and Android app), have you checked your Nextcloud log? Does the Android app show any error message? Did you already try to login with another method than QR code like app passwords or the normal username / password login? Did it work before upgrading the Nextcloud instance? Does the login work with any other device (and with another Android device)? …