Need advice on what to do next

Hi there! As title suggest, I am not sure on how to go on from where I am now. I started programming a while ago, (approxmately 5-6 months ago) and I started with python. In recent months Ive been covering alghoritms and grinding leetcode problems and I am feeling pretty confident with by knowledge of algos and data structures. Although I had fun learning programming with python, my ultimate goal was to create an app for my little brother, I have an idea, I have designer friend who is ready to help me with UI and UX, the only thing left is coding that up. However, I think that python is not meant for software developing? So question is what should I learn next? Many are advising Java, others are saying to try Kotlin. From the professinal point of view, what do you think I should do? Or I am better sticking to python?