When we apply a CSS style on the QHeaderView, in order to position the sort arrow over the text itself, we see that in Qt5 it works correctly, but in Qt6.5.5 this does not work correct. First letter of Headerview cuts off. 

Attach image and an example application where this can be verified. In the image, you can see how in the window on the left (Qt 5.15.2) the sort arrow is perfectly placed over the header text, but in the window on the right (Qt 6.5.5) the position of the arrow is correct, but it conditions the position of the header text, causing it to be displayed incorrectly.

Run the example and click on header view to see the behavior.