It is extremely difficult to measure external air pressure from within a rocket (or any moving vehicle), because air moving over a surface exerts lower pressure on the surface, and distorts the readings. Look up the Bernoulli effect.
Even when in still air, to get reasonably stable air pressure readings with that sensor, you need to average hundreds of measurements.
what is relatively simple way to reliably detect apogee.
Unfortunately, there isn't a simple way.