Thanks to TheWeightOfUwU for finding out how this works

There is a glitch in the character creation that allows starting the game with all attributes at level 6. To execute it, you need to start a new game, select "Create your own" and then press the start key on a controller to open the pause menu. Here, you select "Back to main menu". When you now start a new game again, the initial attributes will not be assigned randomly. Instead, they are chosen from a set of predefined debug statlines. One of these debug statlines has all stats maxed out at 6.

Repeat the process of returning back to the main menu, starting a new game and entering character creation until you get the statline with the maxed attributes.