I can't invert a B&W vector shape. The Effects | Transform | Invert Colors command is grayed out.
It might help if you could share a file that has a shape in it where you can't do this - just to see if it's something in your CorelDRAW installation that is not working correctly, or if it's something in the document.
I tried to insert the file but it gives me an error - here's my screenshot to cut and paste.
The CorelDRAW Community forum software doesn't allow .CDR files to be uploaded.
You could wrap it in a .ZIP file, or even simply change the extension of the .CDR file to .ZIP, in order to be able to upload it.
Or, put the file somewhere on-line where you can share a link to it.
Perhaps it is the case that you can't invert spot colors.
If I Import that PDF and then convert everything to CMYK, I can then invert the result.