FWIW, I’d suggest that the problem here is that Carbide Create is outputting SVGs using pixels as the unit for its dimensions.
The user’s intent is to produce files that represent a design with certain physical dimensions. As such, the output files should be written with physical units.
If you want to get into the value for “correct” DPI, I don’t think there is such a value here. You’re right that the CSS standard (upon which SVG has based its dimension attributes) specifies a “96DPI” reference pixel, however that’s a simplification.
What the reference pixel really is, is:
the visual angle of one pixel on a device with a pixel density of 96dpi and a distance from the reader of an arm’s length
The specification then goes on to elaborate that different reading distances will result in different conversions from pixels to physical units.
So I’d expect to see different physical pixel sizes depending on whether I’m using, for example a laptop (which is closer to my face, say 50cm), a large monitor (which is a bit further away) or a TV hooked up to my computer (which is across the room).
Fundamentally, the pixel is intended to be used for display devices, to produce a design that is equally legible across many different devices (and even print media).
It’s not intended to be used to represent physical dimensions. We have physical units for those.