Buck Converter Ripple Despite using Capacitors?

I'm using a buck converter to step down 12V to 5V, and I've added electrolytic and ceramic capacitors at the output to smooth the voltage. However, I'm still seeing noticeable voltage ripple on the output when checked with an oscilloscope.

I've tried:

• Adding more capacitance (both ceramic and electrolytic)

• Placing the capacitors as close to the output as possible

• Using different load conditions

Despite this, the ripple remains.
What could be the cause of this ripple even with proper output capacitors? Is it related to the switching frequency, capacitor ESR, PCB layout, or something else?