Perhaps looking here, downloading the attached file, and studying the contents may help you in creating "brushes".
Also, you do bot have to use the Calligraphy Tool to make such shapes. You can use circles, ovals, rectangles, and the Pen and Bezier Curves Tools to generate such shapes. Then, you can apply the shapes to paths to yield different results.
Beginners' Questions How to create brushes
Inkscape.org
Hello, i'm a student and like Inkscape for drawing, but i do not know how create brushes. Is there a way to make brushes like in Adobe Illustrator?
Inkscape des not have brushes like Illustrator, it has presets for the Calligraphic Pen tool that can be customized and saved.
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Paths-Creating.html#Paths-Calligraphy
Perhaps looking here, downloading the attached file, and studying the contents may help you in creating "brushes".
Also, you do bot have to use the Calligraphy Tool to make such shapes. You can use circles, ovals, rectangles, and the Pen and Bezier Curves Tools to generate such shapes. Then, you can apply the shapes to paths to yield different results.
https://inkscape.org/forums/tutorials/examples-of-brush-shapes-i-made/