Most of my time this year has been with browser streaming, async Rust, and vanilla JS. I think the last has been the most useful. I highly recommend really learning the DOM. Implement your own client-side routing. Make a view framework. See if you can make an app without a bundler/build step. Or even without npm at all. It's fun.

In general, I think it's very valuable to have a deep understanding of your platform, even if you don't need all that information on the daily.