Created a prototype with desktop dimensions (1377 x 768 px). When the prototype link is viewed on mobile phones, the prototype dimensions are suddenly stretched to the full height of the mobile screen it is being viewed on.
This bug applies across mobile browsers and the Figma app.
In contrast, no such issue exists when the prototype is viewed on a desktop, even when the desktop browser is resized to resemble mobile proportions.
The only workaround I could find at present is to crop the frame/artboard to match the intended prototype resolution.
Management insists, and I’m not in a position to deny their request, though I did mention that the prototype is best viewed on a desktop anyway.
Either way, it is still a bug because the proportion of the viewport should not have changed regardless of which device it is viewed on. Several elements on the prototype also strangely disappear, while there appears to be no issue on a desktop. This is not an issue that other prototyping applications (e.g., Adobe XD) appear to have.