Post some photos of the crank arm and it's connection to the crank axle, so we can see what type you have.

A common type has two smaller "pinch" bolts that tighten the end of the crankarm around the axle. Years ago, I was getting clicking noises: I fixed it by removing the crankarm, wiping the axle splines to clean them, adding a little grease, then reinstalling. That fixed it. See the Park Tool guides for a step-by-step method to remove and install these type of cranks. It has to be done correctly, first by adjusting the bearing preload with the center cap, then tightening the bolts. Easy, once you know how.

I got a creaking noise on my current bike, only under pedal load. I was convinced it was coming from the crank axle bearings. No! it was the rear quick release that creaked with the slight frame flexing. I cleaned the quick release and put a thin film of grease on the cam surface. That worked!