Choosing a certain style in Affinity Publisher

I am currently trying to define a shortcut that selects one of my defined styles in Affinity Publisher. However, as the styles menu is not a system menu but a menu within the application, I'm wondering if there is a way to do this? What would be the right way to define something like this in KM?
Many thanks for your input!

As I don't have Affinity Publisher, can you share some screenshots showing exactly where it is and how it appears? That is, is it a normal menu, something on a palette, something else?

Without that info, it's hard to say how you'd access it.