Hello @Diego Pigola,
Thanks for reaching out!
I am not able to replicate the issue locally, the file uploaded to SharePoint is reflecting immediately when querying from graph API. Please try this API from API testing tools like Postman or Graph explorer with necessary permissions.
Ideally there shouldn't be any delay in querying the files initially (when file is created), but if the issue still persists, I recommend you to raise a support case with Microsoft Graph, a Support Engineer will be able to assist you better. You can raise support ticket from
http://aad.portal.azure.com/ or https://admin.microsoft.com/#/support/requests.
Hope this helps.
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