Keeping in mind what the state of the world is, learning to code or expanding your knowledge in coding sounds like the best thing you can spend 6 months on. There are a lot of free courses out there and some awesome paid ones.

But if you decide to learn a new programing language or something like that, you shouldn't just start studying, but you should start learning how to code in the context of a real world project. For instance, you might want to build a Steem app, a complex website, a desktop application, a mobile application or even do some machine learning, it really depends on your interests. But pick an ambitious project that you like and start working on it from scratch. That's really the best way to learn a new skill - put it to practice on something real.