Yes they are a type of coast, because of the size of the great lakes being comparable to seas even though they aren’t saltwater. It doesn’t meet the maritime concept, which is based on seas, but they are often referred to as either shores or coastline depending on context.

https://en.m.wikipedia.org/wiki/List_of_U.S._states_and_territories_by_coastline

That’s an image from Duluth, MN, the furthest port in the Great Lakes from the ocean. You think boats that big making it up some dinky river? Clearly a coast

Also, the coast guard operates in the Great lakes as well