Hi @laxman ,
With Graph api, you can only get the groups that the user is a memeber of: https://learn.microsoft.com/en-us/graph/api/user-list-memberof?view=graph-rest-1.0&tabs=http
For Rest api, the scope is site, so you can only get the information of one site.
The best way is using search api, sign in as that user,
_api/search/query?querytext='contentclass:STS_Site contentclass:STS_Web' .The user would get a list of the site he could access to.
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