The question is whether Kant’s philosophy is compatible with the Church’s theology. Historically, Aquinas has been used to explain Catholic theology. And Aquinas and Kant disagree fundamentally about metaphysics (at least this is the consensus opinion - although there have been Thomists with Kantian leanings).
How to characterize the disagreement? It revolves around the concept of truth. Kant argues that we can only know phenomena (things as they appear to us) and not noumena (things as they are in themselves) - the assumption being that the phenomena are fundamentally different than the noumena. Furthermore, the phenomena are structured by us - time, space, key concepts such as cause, substance, etc, are “imposed” by us on reality. All of this creates a “truth” crisis - the human mind is no longer the “mirror” of things - we structurally cannot know reality as it is in itself - metaphysics becomes impossible. But how do we know the “truth” about the “structure” - if “structure” is noumenal (which seems to be implicit in Kant’s argument).
And this is not the end of the story. The entanglement of mind and being has continued to be a hot topic from the 19th century (Hegelianism, Marxism, etc) down to the 20th century (phenomenology, cognitive science, quantum mechanics, etc).