LibreCAD has its own Font format for easier and fast rendering.
So I assume, that Inkscape does not support this and is not capable to render LibreCAD LFF fonts.
You can try to create a SVG in LibreCAD, by using File -> Export -> CAM/plain SVG.
Or explode text before saving in LibreCAD. But this converts text into basic entities and you can't modify text after explode.
So it is recommend to keep original DXF with MText and use a DXF copy with exploded text for Inkscape import.
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