I ran into a similar issue today, here is my solution:
Note: I manually created a n8n-uploads folder in my case.
In n8n, using the "Read/Write Files from Disk" action:
File Path and Name: /app/data/n8n-uploads/file.jpeg
/app/data/file.jpeg works out of the box, but I wanted to store all my files in the same folder.
image.png
Here is a video:
https://www.loom.com/share/5e6bccdbd19842a489cc10f90ea871d4