There is a weight, the natural one, that allows you to be relaxed. Dynamics depend on the velocity you impart to the key: the faster it descends, the louder the sound will be. Usually, one is taught to play everything loudly first and then apply dynamics; I do the opposite: I play everything softly, i.e., by lowering the key slowly, because I maintain that only if I acquire the capacity for slowness will I be able to speed up the gesture and achieve a "physiological" forte. Then consider that the piano gesture must be transmitted to the hammer felt, which must perform a fast and elastic movement: a force applied in an unnatural, stomped way (when you see playing from above, by "uncontrolled" falling), imparts a braked run to the hammer at the most decisive moment when the sound is realized, the moment of contact and the fall onto the string. The force does not come from the muscles of the fingers (which are actually in the forearm!) or the arms, but from the shoulders, the back, and the diaphragm. In fact, I tell you that for a decisive forte, the force must come from the anal sphincter, as if you had to perform an evacuative effort. Even the way you breathe is decisive. Try applying the same weight: during inhalation, everything moves upwards (suspension); during exhalation, downwards. Our breath coincides with musical breath: inhalation (suspended sound), exhalation ("visceral" sound), and again inhalation (suspended sound). If you think about it, the leg does the same: during inhalation, little or no pedal; during exhalation, more abundant pedal; the wider the breath, the deeper the pedal sinks, with the possibility of being changed without ever being removed (the "pedal tremolo"). Therefore, the pedal is not just an effect, but it is our breath, the equivalent for the pianist of the conductor's baton or the bow of string instruments. All this while applying the same weight of the arm, which is only a means to connect the fingers to our viscera, the true participants in the piano touch. Try never to feel the bottom of the key (wasted energy, especially in the grand piano), or if you do, your bottom must not correspond to the keybed under the keyboard, but to the hammer felt. Think of the key as your hammer and that you have the possibility of coming into direct contact with the string. Logically, it also depends on the mechanical regulations: there are adjustments that require greater muscular commitment, others (which I prefer) that allow for a more thoughtful and instinctive approach. On this, pianoexpert can give you clarifications. I will tell you one thing: with my approach, it paradoxically becomes harder to play on an "easy" keyboard, because it is harder to manage the "slowness of the key," thus requiring greater dynamic control; therefore, I am wary of adding lead to strengthen technique. The sense of a "heavy key" must be acquired by your mind. With the right weight imparted TO the fingers, you will succeed in feeling a 47-gram key as heavy! Crazy dynamic control!
This is just my way of thinking and playing: listen to other bells [other opinions] as well.