Select a decoupling capacitor
Filters are usually voltage dividers.

A voltage divider has series and shunt components.

Your capacitor is the shunt.

Now insert an overt series impedance: 1K ohm resistor, or 1 milliHenry inductor.

And ..... you must ground the capacitor at the MCU gnd pin at the IC package, or on the ground plane near the MCU.