I find the description of dark matter confusing. I hear statements like "dark matter has negligible interaction with ordinary matter". So, how do scientists kno

I find the description of dark matter confusing. I hear statements like "dark matter has negligible interaction with ordinary matter". So, how do scientists know that dark matter exists? "The answer is that our galaxies spin too fast for the visible matter alone to hold them together. Dark matter, which makes up 27% of the universe, provides the additional gravitational force needed. In contrast, visible matter only makes up 5%." However, I'm left wondering whether dark matter does or doesn't interact significantly with visible matter.