Hi @Pratyaksh Sinha,
Per my test, full control of the site is necessary to retrieve the permission of a site. I have tested user with approval and design permission level to get the list of permission by powershell. And they all return Attempted to perform an unauthorized operation.
We will need a full control permission to get RoleAssignments properties under web.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.