Overview: I have been using Copilot Studio for production solutions for a few weeks now, and I am impressed. I pushed my fist Copilot Studio custom agent from using ALM into QA and Production, where I finished the iteration a week ago. My boss was looking at the Agent in SharePoint and identified a bug with uploading files and using them.
Anyway, I tested the scenario in other channels and in the Test area without issue. In SharePoint, a Custom Copilot Agent can't upload a file to work with OOTB.