So there is generally believed to be huge difference in meaning between Ethics and Morality today, because it is a useful tool to have them mean very different things. Among other things I suggest the TV show "The Good Place" as a useful and fun/funny introduction, but there are plenty of great classes to take and other philosophers to read on the subject.
Morality may be objective [1], but Ethics is not just/no longer only the "study" of morality but the subjective practice and personal application of it. Ethics becomes the pragmatic and imperfect framework for working with the belief system of the other's ideals. If you want an infosec analogy, think "security threat model" versus "security posture". Morality is your ideal "security threat model", many people will have shared threat models and a lot of lofty goals and ideas to guard against them in theory. Ethics is your "security posture", what you are actively doing day to day to guard against threats, not just imagined, but the real ones you encounter on those days. People may share the same "security threat model" but nearly every "security posture" is a unique and personal snowflake with differing imperfections (and sometimes unique beauty).
[1] You paraphrased Immanuel Kant, which suggests to me you may have a strong religious background/upbringing coloring at least some of your view here. Unfortunately, this overall question of if there is an objective Morality is a centuries long debate among Philosophers and people have different perspectives across different religions and in different cultures. Immanuel Kant was a strong voice on the side of an absolute and objective Morality, but there are so many other viewpoints. Defining a truly objective Morality is harder than it sounds, even if there are lots of individual moral beliefs many religions and cultures share together. Especially, I believe, as imperfect people working through however many layers of imperfections we may have accumulated in our personal ethical frameworks along the way to having these philosophical discussions. Because Philosophers can't agree on if Morality is objective and/or absolute or neither, it becomes useful to separate the discussion of the ideal state (Morality) and the subjective practices (Ethics) as separate things.