only the latter
I'm, again, not claiming the absolute absence of a universal morality, just as is no one here is claiming its existence, just that it's unknowable by finite beings whether or not it exists, or if it does, what it is
also, anyone can espouse a supposedly universal morality but they don't work in practice
Kant himself was perfectly fine with colonialism and slavery
by our 21st C standards that's particularly egregious, but there will always be hard points of disagreement and as soon as there's any imperfect resolution there's no universal morality because you and I now disagree about what is moral - what the universal law should be - as regards whatever the issue is
I'm not going to pretend like I can match you (or half the people here, really) in a history of philosophy tangle, but I assume various objections have been raised to the categorical imperative on various grounds
the best I think a person can do is acknowledge that your worldview can't be separated from the context (historical, cultural, evolutionary, etc) that formed it, having acknowledged that use your own best judgement, and live with the resulting doubt
Sure but in the instance of colonialism and slavery, it's egregious to us, and of course we are right to be outraged. Certain old red tories might still see it as a necessary (civilising) evil. The problem with morality is it is a war in a very real sense, hence cannot be universal in any other sense than ontological. There is absolutely a forced coercion element to morality, call it dictatorial if you will.
Kant's weekness is he is trapped in the analytic/synthetic dichotomy, I.E: between definitionally true statements and those which require verification. So in that sense like Hegel, he rests his edifice on consciousness and the consciousness of the self. This is still far too vague and metaphysical... I.E: it's not interesting how we cognise knowledge
but how the knowledge is developed and cognised itself, which Kant struggles to answer.
What interests me about morality is how people in any given moment in time are forced to adhere to it, as a power above themselves. Which is why I think Thomas Hobbes is the most important political thinker before Marx, even if his conception of sovereignty runs diametrically opposite to the free development of each being the free development of all.