imagemagick's convert doesn't recognise Inkscape 1.0alpha's new CLI options
Installing the inkscape development version from the PPA replaces the default system inkscape version (installed through apt or whatever) but inkscape-trunk isn't a full replacement of the inkscape package.
The default inkscape package allows the imagemagick tools to use inkscape as rendering delegate with SVG, and this doesn't work with the inkscape-trunk package.
Inkscape Version and Operating System:
- Inkscape Version: whatever inkscape-trunk installs
- Operating System: Ubuntu 18.10