Here are the results of using this xcf file. It is not an actual brush, but you can open it, Edit-Copy Visible, and as many of you know, it goes to the clipboard and can be selected as a brush. I recommend setting the spacing to 1 and Hardness slider to about 90 - 95 while using this "tube".

Made it into an eye brush.

I downloaded Affinity Designer, contemplating buying those brushes just so I can see how the dynamic brush engine works. Glad you're having fun.

absolutely T for tremendous, racer !

Designer is the vector variant of the Affinity suite. Its mostly a painting and illustrating program. Photo is more the equivalent to Gimp.

Doesnt relly matter because both programs use the same brush engine for pixelbrushes. In Designer you have to switch to the Pixelpersona.
AFAIK, you can use the trial version for 14 days without any limitations, and if i remember correctly its also at a 50% discount while the covid crisis lasts.

EDIT: the trial has been also extended to 90 days

The wispy brush i showcased is from the xenon-brush-pack-bundle.

I thought that I could play here too, in glass of course. A colourful glass smiley brush; makes tubes at 5, 10 15 spacing intervals or just by itself.

I wonder why mahvin's brush has artifacts on the sides, while omg's looks super smooth.

The bump map shading.