I don’t see how that is relevant? You’re already familiar with C, so writing about C does not influence whether you will be outdated in a few years. Learning and writing about Rust could be something that becomes useful, but not necessarily practically - it depends on what you will do in the future.
If you feel you lost your passion, I would suggest learning and experimenting with Rust. It’s different, so may be interesting and thought provoking to learn.
Writing down what you know about C may also be worthwhile, good, or produce a good resource, but I don’t see it as much or like as sparking lost interest and passion. If that is actually your goal (you only asked about future relevancy in the end).
Tell me when you’re getting used to USB so I can prepare for the next switch /s 😅