Most hobbyist FPV drones are DIY and built from individual open source components like betaflight. You can find some of the hardware with open source designs too. Most people in that scene including myself buy the motors and various components to preference and lay out the drone the way we want it. I custom cut my drone frame for instance and 3D print my self designed canopy. About 80% of the software on my drones is open source (the major exception is the DJI VTX).
Do a YouTube search for joshua bardwell he covers how to do this in exhaustive detail.
