@Boopathi Subramaniam,Thanks for posting in Q&A.
From your description, I know you want to know which Intune policy or Group policy blocking access USB Storage on Windows 11 device.
Based on my research, here are some methods you can refer to find which policies has been applied on targeted device.
For Intune policies, you can go to Intune portal, Click Troubleshooting + support and enter the user's name and device' name you want to check, it will list all the policies that has been applied, then you can check which policy has deny access to USB Storage.
For Group Policies, there are some methods you can refer in the following link.
https://www.thewindowsclub.com/find-all-applied-or-enabled-group-policy-settings-in-windows-10
Non-official, just for reference.
Please try above information, if there is any update, feel free to contact me.
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