the folder /Download is part of the shared storage, see also the overview here
It would really help if you provided a screenshot of your relevant blocks, so we can see what you are trying to do, and where the problem may be.
To get an image of your blocks, right click in the Blocks Editor and select “Download Blocks as Image”. You might want to use an image editor to crop etc. if required. Then post it here in the community.
Upload file using Google App Script to Google Drive
I am able to do this for all files except pdf files. I am trying to do this on Android 11 device.
However, I am able to upload all kind of files including pdf files using Android 10 (or below devices).
If required, I can share aia file also.
Below, are the relevant blocks -