Hi biberjustin,
Thank you for querying in this forum.
From your description, it seems that you want to use Upload file option in Microsoft Forms, however, it is greyed out on your side.
May I know if my understanding is right? If so, generally, If you choose to use Anyone can response, you may not select File Upload, if you want to select File Upload, you can only share this form Only people in my organization can respond. As shown below:
So we’d suggest you go to Microsoft Forms > click Share > Select Online people in my organization can respond, then you can check if you can use this option.
If the scenario above is not consistent with yours, you can also post back an provide more details about your situation, and we will also try our best to help you.
Best Regards,
Sukie