Adding Venstar Add-a-wire ACC0410 to HVAC with Nest Thermostat E
Just follow the yellow brick road to your C terminal
Based on the fact that you have a two-wire cable apparently running out to your compressor based on the fact one wire of the cable is landed on Y, we can find your C terminal easily.  In order for the air conditioner to come on when called, its contactor coil has to connect between Y and C as the thermostat applies 24VAC to Y to call for cooling.  So, the other wire from the compressor cable must connect to C, and looking at the labeling on your control board, lo and behold, it does!  Furthermore, HVAC terminal blocks are designed to have 2 wires under one screw, on opposite sides of the pressure plate, so the fact there's a wire already there is no obstacle to your plans.
From there, it's no different than how the videos describe it.