If you want to be a solo/technical founder, I'd consider learning to build web apps a great first step - it's accessible, cross-platform, and flexible. There's also no shortage of resources online. On the frontend, React is commonly used and generally a safe choice. On the backend, some nodejs with heroku or docker should give you a gentle introduction (with the added advantage that you'll be learning the same language for both front and backend -- one less thing to worry about as you're starting).