Oh yeah I actually don’t know how to code. Most I’ve done is build a calculator on android using Java , and a bit of JavaScript. I haven’t actually gotten to the CS stuff in my degree, I’m doing calculus rn. But it’s going to be mobile first, so whatever the best languages are for android and iOS. But yeah it’s all just an idea in my head right now

If you want mobile then consider what platform. If you really want both then you might want to consider a framework like dart, flutter, react native or the new kid on the block lynx to build in a language that can compile to multiple platforms. Start learning about all these technologies now. Then consider pros and cons of each. Maybe make a simple app in each before picking one.