Using EndeavourOS and Vivaldi.

Brushes are much larger than the indicator, extremely "watery" and boxes instead of circles. For instance, the default, round brush becomes a square, dragging it along the editor causes the texture to "seep around" as if it was a slanted canvas and the ink extremely watery spreading much further than the actual brush.

At the same time a small area at the top of the editor is perfectly usable, with the brushes behaving as intended.

The attached screenshot shows the default brush. The small area on top works fine, whilst the rest of the editor is a hot mess.