The most recognizable, and possibly most important difference between dark matter and antimatter, is that what we know of dark matter comes from observations of the very large, and what we know about antimatter comes from observations at the particle level.
Dark matter is believed to exist because, using Einstein’s equations of gravity, the universe supposedly should be much more massive than what all the observable objects weigh. That missing matter is dark matter. Because dark matter is, for us, invisible for the most part, one of the ways it has been observed is when gravitational lensing happens. This phenomenon happens when observable light is bent due to large, unseen gravitational forces, while traveling through space. According to scientists, we can only see about 4% of the real mass and/or energy within our universe, and 22% of the universe’s mass and/or energy is estimated to be dark energy.
Antimatter is different, as it has actually been physically observed within labs, and is not just an estimate. It’s basically just matter that has the opposite charge of matter, which when matter and antimatter come in contact with each other, proves to release massive amounts of energy due to self annihilation. [Example, a positron, or an anti-electron is an antimatter particle with a positive charge, while an electron is a matter particle with a negative charge.] “ It is estimated that energy created from matter / anti-matter annihilation would yield 10,000,000,000 times the maximum energy created by chemical energy and 100 times the energy possible through nuclear fusion. The potential applications for antimatter energy are exciting, although far off in terms of feasibility.”
Simply put, dark matter exists unseen on a ‘larger than life’ scale within the universe, larger than what we can see with our telescopes, and antimatter exists on a basis of very small scales, based on antimatter particles created and observed within our labs. There are no known direct relations between the two.
Source 1. Source 2.
I hope this answered your question!