Here are the steps to control the BTR5 2021 in FiiO Control App.
1. Please update the FiiO Control App to the latest version (Click the link to get the latest Android version: https://forum.fiio.com/note/showNoteContent.do?id=202105071628040377809&tid=17
2. Ensure that the FiiO Control App is the latest version. Enter the settings menu of the App-> Tap "Bluetooth device control"->Tap the BTR5 2021 to complete the connection. After a successful connection, it will enter the Bluetooth control menu.