1.Gravity will not stop the expansion of the universe because the "task" set by nature is to "collect" matter not to disperse. Without gravity, the universe will not exist.
The expansion of the universe is determined by the state of dark energy, which creates conditions for the development of the universe. Newton's third law is in effect here. The matter is converted into energy, and energy is converted into matter. In this process, in the first stage of expansion, matter accumulates in the universe and the universe expands. In the second stage of development, the accumulated matter is converted into more energy — the universe is warming.
2.Gravity isn't a quantum force.
3.The term "antimatter" is a human concept. The correct natural concept is converted matter.
5.There's a part of dark matter that's been discovered. It is known where and what undetected and unknown still dark matter can be.