Why is my DJI Mini 4 Pro flashing yellow?

A DJI Mini 4 Pro blinking yellow quickly has lost the signal from its remote controller: turn the controller on or re-pair it. Four yellow blinks at startup just means it's warming up. Slow yellow blinking means it has no GPS and no vision positioning, so it's in ATTI mode and will drift. Red and yellow alternating means the compass needs calibrating.

Mini 4 Pro yellow lights — Yellow status light meanings from DJI's Mini 4 Pro user manual for the aircraft and the DJI RC 2 controller.

Yellow on the drone

From DJI's Mini 4 Pro manual:

Pattern	Meaning
Red, yellow and green alternating	Powering on and self-testing (normal)
Yellow, four blinks	Warming up (normal)
Blinks yellow slowly	GNSS and vision systems off: ATTI mode
Blinks yellow quickly	Remote controller signal lost
Red and yellow alternating	Compass calibration required

Fast yellow on the ground: the controller is off, out of range or linked to a different drone. Power it on. If it still won't connect, re-pair in DJI Fly under Control > Re-pair to Aircraft and hold the drone's power button for more than four seconds. Full steps are in Mini 4 Pro not connecting.

Fast yellow in flight: the drone lost the link and will follow its signal-lost action (RTH, Descend or Hover, set in DJI Fly's safety settings). Point the antennas at the drone and move to open ground. See drone keeps losing signal.

Slow yellow: in ATTI mode the drone can't hold position and drifts with the wind. DJI says to land as soon as possible. Move to open sky so it can find satellites. Indoors, over water or at night, the vision systems may not position it either.

Red and yellow: calibrate the compass in DJI Fly under Safety > Sensors, outdoors, away from cars, rebar and metal. See DJI compass error.

Yellow on the DJI RC 2

Blinking yellow: the controller battery is low. Charge it over USB-C.
Solid yellow: a firmware update failed. Charge both devices above 20%, restart them and update again in DJI Fly.

Other RC 2 lights: solid red means disconnected from the drone, blinking red means the drone's battery is low, blinking blue means linking, and blinking cyan means the sticks aren't centered.

Red lights to take seriously

Blinking red slowly: takeoff is disabled, for example low battery. Check the prompt in DJI Fly.
Blinking red quickly: critically low battery.
Solid red: a critical error. Don't fly. Read the DJI Fly message, and contact DJI or start a repair if it won't clear.

DJI Fly explains most warnings on screen, so check the app before guessing from lights. A full list for other models is in DJI drone lights meaning, and more on this drone is in the Mini 4 Pro guide.