Your PureOS is tainted. The only versions of gnome-software that we include in PureOS are:
gnome-software | 3.28.0-1pureos1 | green | source, amd64, arm64 gnome-software | 3.28.0-1pureos1 | landing | source, amd64, arm64 gnome-software | 3.28.0-1pureos1 | purple | source, amd64, arm64
The PureOS specific change includes exactly a difference to recognized things from the pureos-main archive as free.
Please reinstall your system to ensure that you actually only have stuff we ship in PureOS, and make sure that no non-PureOS sources exist in your sources.list.
The output of apt list suggests a manual installation of a foreign gnome-software package (highly likely from Debian), but it could also be that it was updated once and the source it came from has been removed meanwhile (if you know that you manually updated gnome-software that is fine, in this case you would need to reset the package and can maybe avoid a reinstallation).