Answer

I don’t think Kant had a subjective epistemology. That is a common interpretation, and in my opinion it is incorrect. He only pointed out the fact (not merely the opinion) that all of our cognition is colored by subjective elements. Every perception is carried out in our own language. But what we still perceive and describe is the world itself. Therefore, this relativity דווקא strengthens the objectivist view. It is like the relativity between different geometric systems, which—contrary to what various demagogues say—is a pure expression of objective truth. Different geometries reflect different realities (curved spaces). There are no two different geometries that describe the same reality (in the same space). And so too with Einstein’s theory of relativity, which describes objective physics from the viewpoints of different systems.