Inconspicuous Guides: A Qualitative Study to Understand the Degree of Intrusiveness in Visualization Onboarding Topics: Human-Centered Aspects of Visualization; Usability and Empirical Studies of Visualizations; Visual Representation and Interaction In Proceedings of the 20th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications - Volume 1 GRAPP, HUCAPP and IVAPP: IVAPP, 706-717, 2025 , Porto, Portugal