Prepare now for Remote Desktop client for Windows end of support

Please, where is official ADMIN documentation for Android version of Windows App for troubleshooting error 0x204 when connecting to Windows 11 machines on-prem? Everything was working few days ago in old app. Now it changed automatically to Windows app and no single one of our users is able to connect to W11 machines which are all on-premise. What is difference in creating rdp connections between old and new app? Where is documentation about security of Windows App (e.g. configuration and usage of protocols etc.)? Thank you for any help. Our organization is stuck. Is there any official way how to use old app on Android devices?