The move from managing categories to leading a function is the point at which a lot of strong careers plateau. The reason is rarely capability. It is that the new role rewards a different set of behaviours, and nobody says so out loud.
You stop being measured on your own deals
Category managers are judged on outcomes they personally delivered. Leaders are judged on outcomes delivered by people who report to them, most of which they will not be close to. Continuing to do the deals yourself is the most common failure, and it is usually rationalised as being close to the business.
The audience changes
Your stakeholders stop being budget holders and start being the executive. That audience does not want category detail; it wants to know what risk you are carrying, what it will cost, and what you need from them. Learning to compress a year of work into three sentences is a genuine skill.
Build the bench before you need it
Leaders who succeed spend a surprising proportion of their time on hiring and development, often before there is an obvious vacancy. Those who do not find that every problem escalates to them, which confirms the belief that they had to do it themselves.
Find people who have done it
Almost everything above is learnable, and almost none of it is written down usefully. The fastest route is a relationship with someone one or two steps ahead who will tell you what they got wrong.