My goto brain game is how many digits of long division I can do just in my head. Usually only like 7-10 cause I'm dumb.

Get into writing your own fiction stuff you're really interested in. My science fiction universe is about the first stage of interstellar colonization. I love working out the technology and what the experience might be like without any fantasy magic involved. The best part is the positivity that comes with imagining a distant future and what is actually possible. It creates perspective about where we are actually at now and how limited it truly is.