Hello @ninest, welcome to the forum !
From what I remember from Now.sh/Vercel, it’s used to serve static frontend pages, but Streamlit apps are not purely frontend applications because there’s a Python server running in the background and this cannot be launched by Vercel.
Check this answer for reference. Basically you need a PaaS which can run a Python server (Streamlit) to deliver your frontend app connected to the Python server, which is better done with Heroku, AWS, GCP, Azure…