Analysis: Early work
This looks like very early work as when enabled (by using a Windows configuration tool with the mentioned preview build), the feature only shows colored blocks as the graphics for each category. We assume the four colored squares shown will host the icons of four apps from each category (maybe your most-used apps in every category, or that’s the first thought that occurs).
Of course, we don’t know how the interface will be realized, and this is just guesswork. We also need to firmly remember that as this is so early in the work towards this feature – it’s not properly implemented at all, and hidden in testing – it may not ever see the light of day in Windows 11.
After all, the grid view for apps in the Start menu is in testing as well, as mentioned, and so Microsoft might just decide a category view isn’t necessary – and that switching to a grid layout might be convenient enough for this part of the Windows 11 interface. Then again, more options don’t hurt, and the idea of organizing apps into categories might be an appealing way of rifling through installed software in the Start menu – we rather like this potential move.