I work at ByteDance (though not for long). Most of the "sexy" part of the app is native, or C++ crossplatform for things that would normally be in C++. I'm not sure I'm allowed to share what Lynx is used on, but it's a small subset of the app.
What I assumed from the podcast is that there's a lot of internal reusable tools in C++, and the web-based stuff is mostly about the UI layer.
Is there a lot of WASM to use both at the same time?
There's a lot of internal tools. I don't know what they're written in. I would not be surprised if it's Lynx, but I'm a mobile developer on the TikTok app, and haven't ever looked into it.
I haven't come across any WASM in my time here, but I'm not in a position to declare that it doesn't exist.