When you say ‘smart bulb’ what do you mean? If you have a ZigBee or such like lamp, then that won’t work, it need to be a ‘dumb’ dimmable lamp.
Edit: just to be clear when I say ‘dumb’ that can still be a electronic lamp like a LED, it just can’t be ‘smart’ IE ZigBee, z-wave or WiFi these must have full voltage 24/7 and then over data they dim up and down. A fibraro dimmer is a phase dimmer so reduces the voltage to reduce the light output.
If a light flickers it is usually because your using a none dimmable lamp and you a stretching the driver to work harder than possible to keep the lamp voltage the same (that’s it’s job). If it hardly dims or jumps from 100% to off this is usually because the load of the lamp is smaller than the dimmers minimum capabilities, that’s when you need a bypass. This is hightend when you don’t have a neutral at the switch, as it gets a potential difference from the higher load of the lamp and so can’t run its self.