Ask HN: Where/how to learn mobile app or hybrid app development

Hi I am a startup founder with a previous software background, I am thinking of building my own mobile/hybrid app for my platform since developers are expensive. It will be a fairly complex app. But I only know C/C++/Python (10 yrs in dev) and have been a backend developer with some exposure to web dev (I know Flask and some python django/nginx stuff- have built a couple personal fun easy to medium complexity apps). No idea about mobile apps or hybrid apps. I am also not working so no community. Where do I start? How do others do it? I am thinking React Native or React with a Flask backend but not sure. Please help.