Imagine if, in addition to Scrolling's "Viewport Height" option, there was also a "Auto" checkbox that would vertically scroll the artwork to suit the device width.

This! And also fix something to the "top" or "bottom" edges of the viewport (like nav or tab bars). Great InVision functionality that I miss a lot.

First, download the "Working Scale" app onto your Android device. ... Open the app and wait until it's ready to start weighing objects. Carefully place the object you want to weigh on the post-it (a coin, for example). The app will soon display the weight to the nearest microgram

------------------------------------------------------------------
lil peep merch store>>>>>>> https://peepmerch.store

Think of an "Auto" checkbox alongside Scrolling's "Viewport Height", that would fit the artboart to the device width, with free vertical scroll.

Considering screen sizes vary wildly in every scenario we design for (design review, user testing and of course, production), it would be much better to be able to define the design only in terms of the artboard's width, and the fullscreen prototype preview would fit the design proportionally to the device width, and scrolling vertically using the device's viewport height (not a fixed one).

This is the default behavior for the HTML world, the very presence of a dotted line as a fixed scroll "fold" may even influence designers backwards into thinking that line even exists or should. I believe many designs need to account for the absence of this exact height.

There is an old similar issue, but I tried to be more specific.
https://adobexd.uservoice.com/forums/353007-adobe-xd-feature-requests/suggestions/15038256-dynamic-scrolling-viewport-height-based-on-screen

Yes please. make this happen

At my agency we don't necessarily design at the exact dimensions of the phone we preview with. This results in pillarboxing (a black border around the entire screen). For example, we will create pixel perfect grids that make our workflow much faster, but it makes the screen size something like 360px wide. When previewed on an iPhone 6/6s/7, which has 375px dimensions, there is a border around the screen.

Adding an option to scale the design to match your device's width would solve the problem.