Why don't you just transpile the frontend Python code to JS at build time and just have normal HMTL/JS/CSS in the final deployed web app with a Python backend?

You've mentioned no-code tools. For a client, I had to work with the no-code tool Bubble a lot. They do something similar, where the front-end is not built statically but dynamically and uses WebSockets to communicate with the back-end. I don't think this is a good idea (and that's why Bubble is also trying to switch to static pages now, but you can imagine what it takes to do that once you reach a certain size).