As with many metaphysical and religious questions, Kant thinks they lie beyond our power to answer them. If you can't stand the frustration involved in accepting this, and insist on finding some more stable position which affords you peace of mind and intellectual self-complacency, then you will find Kant's position "problematic" in the sense that you can't bring yourself to accept it. You may try to kid yourself into accepting either some naturalistic deflationary answer to the problem or some dishonest supernaturalist answer.

Kant thinks that a free will is a will under moral laws and that freedom and the moral law are distinct thoughts that reciprocally imply each other. Fichte thinks they are the same thought.

Kant does not think that along with choice of an action we also choose in each case the motive from which we do it. He thinks all is well if I act beneficently, realizing that it is my duty but also having sympathetic feelings for the person I help. But I ought to strive to be the sort of person who would still help even if these feelings were absent. And it is such a case that he presents when the sympathetic friend of humanity finds his sympathetic feelings overclouded by his own sorrows, and still acts beneficently from duty.

I do not know how much my own work has achieved, and I must not pretend it has done more than it has.

Empiricist philosophy always tends to be anti-philosophy (and is often proud of it).

Kant was a rational theologian. He did not pretend to be a biblical or revealed theologian.

The Russian revolution did not occur until a generation after Marx's death. He was not involved with it, or with what came after it. His works do not describe post-capitalist society, and a fortiori they do not recommend any part of what the Soviet Union did.