Trying to display an HTML file in Anvil, how to do it?

You didn’t do step 1 (write the HTTP endpoint). Without step 1, step 2 (the iframe) won’t work.

The HTTP endpoint would be half a dozen lines of code at most.

Honestly, though, I would never approach a mapping feature the way you’re doing it, using a collab notebook and a library that produces an HTML page. I’d integrate a map using Javascript mapping libraries, such as Google Maps, MapBox, etc. That would be more work but would integrate into the web app much more cleanly.

But hey, you do you. If Streamlit works better for you, go for it.