According to the Graph Api, /me
endpoints cannot be accessed with application permissions, please use the delegation permissions Sites.Read.All or Sites.ReadWrite.All, See the link below for details:
https://learn.microsoft.com/en-us/graph/api/sites-list-followed?view=graph-rest-1.0&tabs=http
By the way, using delegation permissions requires the use of auth code flow, for which you can see the link below:
https://learn.microsoft.com/en-us/entra/identity-platform/v2-oauth2-auth-code-flow
Hope this helps.
If the reply is helpful, please click Accept Answer and kindly upvote it. If you have additional questions about this answer, please click Comment.