Are there any places where I can host full stack websites for free?
There are a few services that allow for this, but it depends on the technology stack.
Some services are:
Heroku,
Vercel.
Other cloud platforms may also offer free trials, and free forever plans for limited bandwidth, or build times.
I believe that Heroku got rid of their free project hosting.
Glitch, Replit but they do sleep if the app is not active enough.