Before installing the Trados Studio 2021 SR2 users should clean up the plug-in folder in order to avoid errors caused by the incompatibility between the old plug-ins and Trados Studio 2021 SR2. 

1. Close Trados Studio 2021 CU8 or any older version you are working on now.
2. Go to C:\Users\%username%\AppData\Roaming\SDL\SDL Trados Studio\16\Plugins\Packages 
or paste %appdata%\SDL\SDL Trados Studio\16\Plugins\ in Windows Explorer and press Enter
3. Rename the Plugins folder to Plugins_OLD
4. Install Trados Studio 2021 SR2
5. Install the plug-ins you were using from the RWS AppStore. Make sure the version is compatible with Trados Studio 2021 SR2