I'm glad to hear you solve the problem ,if you have any issue about SharePoint, you are welcome to raise a ticket in this forum.
By the way, since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others." and according to the scenario introduced here: Answering your own questions on Microsoft Q&A, I would make a brief summary of this thread:
How to upload a .csv or .xlsx file to a SharePoint site using the Microsoft Graph Files API
Issue Symptom:
Upload a .csv or .xlsx file to sharepoint site by graph. And will get error that file is corrupted and cannot be open
Current status:
Use [System.IO.File]::ReadAllBytes() upload file to the SharePoint site and keep the file intact
$Content = [System.IO.File]::ReadAllBytes($Filepath)
You could click the "Accept Answer" button for this summary to close this thread, and this can make it easier for other community member's to see the useful information when reading this thread. Thanks for your understanding!