Is it doable ?
I’m trying to populate a Google form with a link to an image (one of my column).
The user insert a file, I get the link to that file then I will be able to use it in my google form virtual column.
Any guess ? 
So you have a Google Form connected with an AppSheet app.
Now, I feel like you have a lot of mixed concepts. Can you explain the workflow as detailed as possible?
For example, what you mean with “google form virtual column”??