Hi @GoodResource ,
As per my knowledge I'm afraid it is impossible to restrict team member or owner not to be able to upload files to SharePoint Online site. This is by design under Teams and SharePoint integration. You can submit your feedback to MS here: https://feedbackportal.microsoft.com/feedback/forum/06735c62-321c-ec11-b6e7-0022481f8472. Customer feedback is very important to us – your ideas can change and improve products for users around the world.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.