Mastering the UI / Cross Hotbar
Access the Character Configuration menu, then select the Hotbar Settings tab from the column on the left. Select the Custom tab, and under Expanded Hold Controls, check the "Enable WXHB with simultaneous LT and RT (L2 and R2 on PS5™/PS4™) double tap" box, then select the "Enable directional and action buttons" button.
This will allow you to use the directional buttons with the double cross hotbar, giving you access to a total of 16 additional actions.
Action buttons only
Directional and action buttons