Firstly try to update your OS.
Resetting the Xbox app from the Settings menu can help resolve corrupted app data. Here are the steps:
Click Start then Settings.
Select System.
Select Apps & features.
Find the Xbox app and click Advanced options.
Click Reset.
Click Reset again to confirm.
Restart your device so that the changes will take effect. Now try to update the Xbox app...
Regarding MS Store issue:
Select Start > Settings > Apps > Apps & features.
Select the More icon next to the app you want to fix
Select the Advanced options under the name of the Microsoft Store app > select Repair /Reset.