Top notch comment.
I chose Rails 14 years ago and have been riding that train ever since.
If I were choosing a new space and starting out, I’d contribute to Kubernetes. Lots of need in that space and I’m sure you could demand top dollar once you have a few merged PRs under your belt.
It can be hard to find an opening to contribute in a decent OSS project that one can keep up with, especially as a beginner, with many others clamoring to do the same.
I don't know about Kubernetes, but lots of large and well-managed projects have issues labelled as "good first issue" to help you know where to start.