I found some interesting threads on Reddit of people running a solo adventure on Foundry for themselves to get the feel of the system down. These were also people new to Foundry so they wanted to get used to that too.
When I first started, I imported the PDF for one of the free RPG day adventures (Fistful of Flowers I think, which is a 10/10 adventure name btw) and used the basic icon PCs from the Beginner Box to build a party of 4. I ran a few combats to get the feel of the system and figure out how to navigate journal entries and such. No idea how feasible that scenario is in FG. Do they make the free RPG adventures available?