How does your WSGI application get deployed within Vercel using mod_wsgi? I thought Vercel was more a solution for static hosting or apps which work with Node and Javascript, not Python WSGI applications.
The key thing is that if you are indeed using mod_wsgi, it is not likely configured correctly and not using correct Python virtual environment or something where Django is installed. I can't easily guess though as I need to know how Apache/mod_wsgi runs on Vercel and how you have configured it. So more information on that will help.