FTL, no SVG settings in Xara for this.
You can post process through https://jakearchibald.github.io/svgomg/ with all options on and get:
Code:
<svg fill="none" fill-rule="evenodd" stroke="#000" stroke-linejoin="bevel" stroke-miterlimit="10" stroke-width=".5" font-family="Times New Roman" font-size="16" overflow="visible" style="font-variant-ligatures:none" viewBox="0 -2860.5 1875 2860.5"/>
I would have though as <def> is not referenced there is no fetch made but it might be as I already have the font.
So I retried with Advent Pro and I could see no action. Dropping it back into Xara just created @import calls in its CSS file...

Acorn