I was honestly unaware of the difference. Upon looking up the term on Wikipedia, the first line is "Institutional racism (also known as systemic racism)." Every subsequent article I looked at under the google search "systemic racism vs institutional racism" seemed to make roughly the same equality.
I'm under the impression that institutional refers to specific formal institutions, like policing, jobs markets, etc. Systemic refers to that plus informal cultural biases, that is institutional is a subset of systemic.