Hello,

I am new to Inkscape but I really like the look of it. However, I use a wacom stylus, and eventhough I could link pressure to the width of the calligraphic tool, I did not find out how to link pressure with its opacity nor to any other stroke property.
Can you help me please?

Teapot

It's not the nature of vector to allow what you are asking. A single "object", such as that drawn with the calligraphy tool, cannot have varying opacity. Likewise, it cannot have a varying stroke. This is a limitation that is true to all vector software (i.e. Illustrator, Corel Draw).

Whilst you can't control opacity with a tablet, you can manually control the opacity of an object using gradients or masks.