A bulb often has a smoothing capacitor built in
, which will stop flicker, but the capacitor with some bulbs would be bigger than the bulb, these two G9 bulbs
the larger one has the room, the smaller one does not, but the larger one will not fit inside the glass cover. So much depends on the type of bulb used.
What is dimmable? I can dim a bulb with a resistor, or capacitor, and it is unlikely to cause the bulb to flicker, but in the main we use wave form chopping, either leading or trailing edge, some bulbs work better with leading, and some with trailing, and some dimmable smart bulbs connect to a wireless dimmer switch or phone. They will all dim, but using different methods, and in the main since an LED when dimmed with old style dimmer switch, does not change colour temperature, in the main we use smart bulbs, so it can give the ambiance required.
In the main, to ensure it dims, we need to keep to the same make of dimmer switch and bulb. We can be lucky, but it is luck.