I updated from Vapor 3 to 4, and Xcode 11 to 12. Now Leaf cannot find my *.leaf templates. I get a "noTemplateFile" error.
I found the answer here: https://theswiftdev.com/how-to-create-your-first-website-using-vapor-4-and-leaf/
The trick was to add a "Custom Working Directory" in the scheme's options. I added my project's root directory and it worked.