SVGs render to an empty PNG

I have a couple of SVG files that I wish to convert to PNG or JPEG - doesn't matter really. Unfortunately, whenever I try to render them to JPG or PNG using CairoSVG, the pictures are empty (contain nothing). I am not sure where the issue is, but actually, when I try to do it online using any other SVG -> PNG tools, the same thing happens. Would love some guidance as to why this is happening.

I have included three SVG files here as an example that you can see in SVG-Viewer.

[N-Sqaured](https://www.svgviewer.dev/s/i90w8yIl)
[Additions](https://www.svgviewer.dev/s/WG1fubcd)
[3x3](https://www.svgviewer.dev/s/nOUOc6TW)

So, yeah - what could be the reason for this issue?

Start by reproducing the empty PNG/JPEG output with the three linked SVG examples using CairoSVG, then compare the rendered result with the SVG viewer output. Inspect the issue discussion for any identified SVG features or constraints; done means documenting the confirmed cause and a reproducible fix or clear limitation.

Written by the indexing model from the issue text.