Ask HN: What is the best stack for real-time collaboration web apps?

I'm scoping different languages, and their frameworks, for their ability to build web applications with real-time collaboration (AKA multiplayer mode, a la Google Docs / Replit).

For context, I will use the stack to build a Leetcode-style sport coding application that enables pair programming in 2-on-2 ranked matches.

I am familiar with Python so Django seems a natural fit. However, other forums have reported Django's limited async capabilities. I also looked into Yjs, but would prefer to avoid JS-land as I will be working solo. Multiple sources have recommended Elixir with Phoenix— learning a FP language appeals to me and LiveView seems a nice way to avoid JS.

I would like to get the HN community's take. What tech stack would you use for this greenfield project?