New posts in Appstream

appstreamcli: AppStream system cache was updated, but problems were found: Metadata files have errors: /var/cache/app-info/xmls/fwupd.xml

E: Problem executing scripts APT Update::Post-Invoke-Success error during apt-get update

What is AppStream? Why is it installed? What is it doing?

appstreamcli hanging with 100% CPU usage during update