Hello @Andre Gouveia ,
Hope you are doing well.
As per documentation, site-search,
One of the following permissions is required to call this API.
Delegated (personal Microsoft account) permission is Not supported for graph API
GET https://graph.microsoft.com/v1.0/sites?search=*
I also try to run above graph API and able to get expected response as shown below so unable to reproduce this issue.
Hope this helps.
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