"Systemic racism" is about the quiet, daily, "small" racisms that most people don't notice or pay any attention to.
As an example, consider the ban on affirmative action programs, while leaving in place things like legacy admissions. The latter isn't isn't explicitly racist, and yet it tends to benefit the people who come from families admitted at a time when they were explicitly racist.
That's just one of countless possibilities. Each one is, potentially, easily dismissed as unimportant. But there are a lot of things that, collectively, add up to serious problems for people who have been historically disadvantaged on the account of their race.
It's sometimes called "racism without racists", because it disadvantages some people even without conscious dislike of them. We started talking about anti-racism a decade ago or so, when the swastika-wearing white nationalists were excluded from practically all polite society, but that systemic racism was still causing a lot of problems. It was different from merely being not-racist, but seeking out the hidden causes of disproportionate effects.
Since then, just plain white nationalism has had a stronger resurgence. And a lot of people who consider themselves not-racist have a tendency to say, "Well, they've got their right to be racist as long as they're not being violent", ignoring the ways that threats are hard to prosecute but still have consequences. They get to consider themselves non-racist because at least they're not actively wearing white robes and using racist slurs.
A lot of people still don't want to do business with explicit racists, and they scream bloody murder about it, even though it's exactly the same kind of free-association that the racists are relying on that somebody will support them.
The effect is that we're dealing with both explicit racism and systemic racism at the same time. They're different and sometimes opposed, even though they also bolster each other.