Since a drone is really a small control system, it likely is either a Microcontroller (MCU) or a Digital Signal Processor (DSP). It is NOT a CPU since it doesn't require : a lot of memory, video for control (cameras and video are separate controllers), ethernet, or large operating systems (Linux, MacOS, Windows, iOS, Chrome, Android, etc). You would NOT use a GPU or need an SoC either.

A DSP would do well, but the ARM Cortex M4 and M7 MCUs have DSP functions within them. They are MCUs not a typical DSP, since DSPs are usually relegated to large DSP tasks these days.

The TI TMS320C2000 series *were* DSPs historically, but TI rebranded them as smart MCU controllers.

I think that either of these options would be a good starting point. And also consider a Real Time Operating System (RTOS) as well. There is a open-source FreeRTOS available too !