Dear Ondrej,

Sorry, I cannot explain anything about Windows. I've used it only when I had to for presentations. Usually, I've encountered rasterization in Export[] when there is difficulty representing color and alpha (gradients in particular) in the target file format. The use of VertexColors is a common cause of rasterization. But sometimes it has to do with other things, such the robustness of the converter or the way it is being used. If you haven't, try asking WRI directly (through the menu, Help > Give Feedback...).

Interesting. I have v14.0 for Mac, and it works. It seems to be the Windows v14.0 version that is having trouble. SVG files are just XML, and can be opened in a text editor. Looking at your files, I can see that the Windows one has got a raster image embedded in it. But interestingly, it also seems to have e a lot of vector info as well!

Why don't you try a simple example, such as the one from the documentation? You can skip a step by using ExportString to see the actual XML produced.

ExportString[Graphics[{Red, Disk[]}], "SVG"]

How do you know the SVG is not vector? When I run your code, and open the resultant SVG image in a browser, not seems to scale infinitely like a vector. It is true that if I Import it back into Mathematica 14, it does import as a raster, but that I think is a limitation of MMA.