Hi @Hirdesh Baghel,
Per my research, currently there is no such offical document support Get-PnPSubWeb require permission. But in graph api, if you want to list the permission of a site. You will need at least Sites.FullControl.All permission. Please refer to the following document
https://learn.microsoft.com/en-us/graph/api/site-get-permission?view=graph-rest-1.0&tabs=http
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