Lots of no-name or DIY drones use flight controller running a BetaFlight [1] firmware, which is open source and quite hackable. If you want low-level real-time programmatic control (like manipulating servos, lights or camera), that is most likely the easiest way. There is also ArduPilot [2] firmware, which is focused more on the high-level control (like managing GPS waypoints and autonomous takeoff/landing).
In both cases you can piggyback your control signals using standard radio or use serial port via dedicated wireless bridge.
Any reason BetaFlight doesn't appear to have even basic pre-shared key symmetric encryption? Some ciphers aren't that CPU intensive.
For nearly 50 years theorists believed that there exist problems taking t steps that also need roughly t/log(t) bits of memory.
(The Quanta magazine article https://www.quantamagazine.org/for-algorithms-a-little-memor... gives some context: for a long time, the best result was t/log(t) as proved in "On Time Versus Space" https://dl.acm.org/doi/10.1145/322003.322015 by Hopcroft, Paul and Valiant in 1975.)