PDF export rasterise/flattens text and vector graphics under certain circumstances.
In some circumstances everything is flattened/bitmapped even if Rasterise/Unsupported properties is selected. PDF should of course never ever rasterise if you not specifically tell it to (that you have an option for, ”Flatten”). This is a serious problem that needs to be addressed properly. As switching InDesign user (and several other DTP apps), you have to rely 100% of the PDF export.
The problem is reproducible (I spend several hours to figure it out):
If i.e an Affinity Photo image is placed in a Publisher document, and the photo has adjustment layers, PDF flattens the whole page. If the adjustment layers is disabled, it works just fine. I've attached documents.
There is also a workaround: If photos, text and vector graphics are placed in separate layers, it also works.
PDF_rasterised.pdf
PDF_rasterised.afpub
PDF_not_rasterised.pdf