Writer rasterise vector images at PDF export

I have previously made technical documents that contain vector images (mostly in WMF format). Now I am returning to update some of these, but all the vector images convert to rasterised images when exporting to PDF. I have tried embedding images instead of linking, and even switching over from WMF to SVG with no luck. The rasterising renders the small text in these technical images into a mess that looks awful on-screen and barely readable on paper. In all and all, all the lines are fuzzy looking and not pretty like they used to be.

I was unable to track which version of LibreOffice I previously used to create these (or was it OpenOffice, can’t be sure of that either). It is also possible that I did not use the embedded PDF export function at all, but Adobe PDF writer since I remember struggling with large file sizes, but that was a no-go this time too. Either way, I am not able to duplicate the quality of images I previously have had, and I’m lost where the option to not rasterise vector images is. Am I missing something?

For the record, I updated LibreOffice to (Windows x64 build), but it made no change.