29 October 2020
Let us address the crux of the question - the physics.
Electrical energy is stored in electric and magnetic field flux. In a capacitor, this energy is stored in the electric field lines that bridge the dielectric between the plates.
The charge on each plate is, conceptually, equal and opposite for a given measured potential. In fact, on one plate there is an excess of electrons (over and above the charge balance in the protons and electrons comprising the atoms of the metal), and on the other plate there is a deficit of electrons (conceptually 'holes' is you like). The opposite charges are attracted to one another, but can not neutralize owing to the surface energy barrier at the junction between the metal plates and the dielectric. The field lines express the force each charge experiences. The distance between the plates times the force is the work (energy) required to separate the charge, scaled by the permittivity of the dielectric.
The density of electrons on the negative plate is larger proximal to the dielectric, and is likewise smaller on the positive plate.
If you connect a capacitor in series to an infinite impedance amplifier input, the input will not load the connected plate. The signal on the amplifier input will faithfully reproduce the input signal at all frequencies for an ideal capacitor, irrespective of the charge state of the capacitor.
The voltage across the capacitor will be fixed and unchanging.
In practice, there is leakage with some characteristic high impedance, typically on the order of a mega-ohm or more. Therefore low frequencies will be attenuated, since the slowly changing waveform will permit time for the plate attached to the amplifier to charge and discharge. This is a high pass filter, and it is commonly found coupling different stages of a multistage amplifier.
If the capacitor loads a signal line by connecting one capacitor terminal to ground, or any fixed voltage, a low pass filter will result. For example the distributed capacitance of a transmission line reacts with the distributed resistance to attenuate high frequency signals. In a transmission line there is also distributed series inductance which acts as an additional low pass filter.
The resistance, or impedance, is a measure of the average collision frequency of a charge subject to an electric field traversing the material. In a low impedance material the drift velocity is higher owing to infrequent collisions, and in a high impedance material the drift velocity is lower so charging takes longer, i.e. is delayed. When a signal is changing rapidly (high frequency) the charge carriers are mostly just wobbling back and forth due to collisions.
In the first case, this prevents charging from attenuating a signal, and in the second case, this causes a signal passed by the line to be attenuated by preventing the distributed stored charge from changing appreciably.
Ultimately, these delays, inductive or capacitive, are a consequence of the necessity to change the stored energy which is done by changing the magnetic or electric field. The limiting factor is the speed of light which will be lower than the free space value in a high permeability or high permittivity material.