I could be wrong, but I don't believe the powershell sharepoint module is a requirement for interacting with Sharepoing online in powershell. It definitely makes it easier, but since Sharepoint has a rest api that you can interact with using tools like postman that have no sharepoint add-on, you presumably could create a regular Invoke-RestMethod call against the api in powershell, no special add-ons required.
If above and the power-automate ideas don't work for you, you could simply FTP the file back on-prem where you have a file-watching service ready kick off a powershell script on a server that has the sharepoint module installed to upload the file to sharepoint.
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Andrew Scheevel
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