My choice is Flutter(https://flutter.dev/). I think it's a good contender when it comes to mobile development.
Music! I am 30 and have spent my whole life not learning any music or instruments because it is 'too hard'. But now I am getting into music theory and wow it is really interesting and awesome. Highly recommend.
I found this video really helpful - https://www.youtube.com/watch?v=rgaTLrZGlk0.
Most modern web application development is via top-down JavaScript frameworks that target the DOM. Developers learn derivative technologies that abstract over & treat the DOM like an end-target that they are free to orchestrate / control.
Custom Elements make it possible to have the page be entirely defined by tags, a growable/extensible set of tags. Instead of top-down systems of interaction, different components on the page can watch & adjust as their children change, or react to events that bubble/capture through them.
It's a long way off, but we can start to write into the page components that express the page's machinery. Right now, those systems are pure code, but we can reify their existence onto the page. Via Custom Elements, computing becomes expressible. You should learn custom elements. Few other experiences out there will give you as direct a connection to the base material & wide powers that are the world wide web.
Another technology I found interesting too learn is ITK (https://itk.org/). You need a different mindset using ITK than other image processing libraries.
Lisp is cool as well.
And fully homomorphic encryption.
Keeping bees is nice as well. One of the best technology invented 9,000 years ago.