Which resolution should I design my game for?


Which resolution or ratio should I design my game for? I want the camera to remain “portrait”.
Is 720x1280 okay or should I build it for a ratio of 9:16?
Will I need to provide multiple builds with different resolutions or do I have to change the resolution through in-game programming?
Which reso’s do you guys publish on?
I’ve been stuck for a while with this one and have been getting “It depends on your blablabalbalabla” answers everywhere I go on the web.