How Tangible is Dark Matter?

How tangible is potential energy??
In a test subway, the floor is laid out very slippery (bad weather). At the very front center is a suitcase filled with heavy stones (or gold bars from Winterheim's possession). The suitcase is supposedly attached to a string. This string is coiled on a shaft connected to a generator. This generator also charges a battery..
Now I accelerate the subway at a constant rate, at least until the suitcase hits the back. The suitcase's potential energy is thus slowly and largely stored in the battery. The suitcase initially weighs the same as it does afterward, as seen from the subway passenger. Seen from the outside, it is of course (relativistically) heavier, as the subway has gained speed. However, its weight is no different than if it had always been at the back. No wonder physicists haven't yet discovered an ether. The potential energy is still included in the total weight of the system; after all, it is ultimately located in the battery and is not negative. One might think that more distant objects in an accelerating system have more potential energy. But the system could be moving toward me. However, all objects move away from me after a certain amount of time, as long as they are in a straight line.

This also applies to the gravitational field. A large cloud of dust in space is supposedly placed in a heat-tight box. When the dust condenses into a star, the potential energy is converted into temperature. The weight or mass of the box and its contents does not change.
The potential energy does not appear to be locally determinable, but it contributes to the overall system mass.* Dark matter is not found locally because potential energy has no inherent inertia or viscosity. It is only noticeable from a distance through gravity.

*Perhaps also applies to the background mass in the TOHM- theory.

Ludwig Resch