"no metadata URIs for vendor-directory" and "could not open appstream://org.kde.kdeconnect.app" are entirely unrelated. For the former see https://bugs.kde.org/show_bug.cgi?id=462931

> could not open appstream://org.kde.kdeconnect.app

There is no appstream component named org.kde.kdeconnect.app, there is only org.kde.kdeconnect

With that in mind it's very weird that this is opened at all?

Can you run "appstreamcli search kdeconnect" and paste the output here?

> Can you run "appstreamcli search kdeconnect" and paste the output here?

Someone else did it on Arch:

Identifier: com.github.bajoja.indicator-kdeconnect.desktop [desktop-application]
Name: Indicator-KDEConnect
Summary: AppIndicator for KDE Connect
Bundle: flatpak:app/com.github.bajoja.indicator-kdeconnect/x86_64/stable
Homepage: https://github.com/Bajoja/indicator-kdeconnect
Icon: com.github.bajoja.indicator-kdeconnect.png
---
Identifier: org.kde.kdeconnect.sms [desktop-application]
Name: KDE Connect SMS
Summary: Text Messaging
Package: kdeconnect
Icon: kdeconnect_kdeconnect.png
---
Identifier: org.kde.kdeconnect.nonplasma [desktop-application]
Name: KDE Connect Indicator
Summary: Display information about your devices
Package: kdeconnect
Icon: kdeconnect_kdeconnect.png
---
Identifier: org.kde.kdeconnect.app [desktop-application]
Name: KDE Connect
Summary: Make all your devices one
Package: kdeconnect
Icon: kdeconnect_kdeconnect.png
---
Identifier: org.kde.kdeconnect [desktop-application]
Name: KDE Connect
Summary: Seamless connection of your devices
Bundle: flatpak:app/org.kde.kdeconnect/x86_64/master
Homepage: https://kdeconnect.kde.org

Whereas on Fedora I get:

Bezeichner: com.github.bajoja.indicator-kdeconnect.desktop [desktop-application]
Name: Indicator-KDEConnect
Zusammenfassung: AppIndicator for KDE Connect
Paket: flatpak:app/com.github.bajoja.indicator-kdeconnect/x86_64/stable
Homepage: https://github.com/Bajoja/indicator-kdeconnect
Symbol: com.github.bajoja.indicator-kdeconnect.png
---
Bezeichner: org.kde.kdeconnect [desktop-application]
Name: KDE Connect
Zusammenfassung: Nahtlose Verbindung zu Ihren Geräten
Paket: kde-connect
Homepage: https://kdeconnect.kde.org
Symbol: org.kde.kdeconnect.png

So it appears that Arch has extra appstream components that are not part of the upstream metadata in KDE Connect. During search we then match the org.kde.kdeconnect.app component, but actually opening it in Discover results in it not being found (perhaps because of missing packagekit backend)

@Antonio can you please clarify whether Arch does something special wrt appstream here?

(In reply to Nicolas Fella from comment #3)
> @Antonio can you please clarify whether Arch does something special wrt
> appstream here?

No, appstream generator also indexes desktop files for applications that don't provide appstream data (such as kdeconnect-app). I guess Fedora has this disabled.

Hey guys, 

thank you for chipping in on this.
A-lot of googling and experimenting later I've managed to resolve this partially.

by default KDE Plasma on Arch Linux doesn't install packagekit-qt5 or appstream-qt it seems. So I manually installed both and the list of applications available in discover is now listed. Outside of that I still get the meta data error however if I close it now I can access the stuff in the list and install KDE Connect. I haven't set it up and used it yet but it does install.

in answer to your statement Nicolas that it was weird it opened at all. The welcoming wizard actually points you to it and says you can use KDE Connect etc, etc... so I presume it's actually meant to be there?? I'm not sure, that's just conjecture but it's odd they'd mention it and it not be there. 

Anyway I have it working for now, but I would like to find a resolution to the popup message re: metadata and to remove that if you guys have ideas?

(In reply to Nicolas Fella from comment #1)
> "no metadata URIs for vendor-directory" and "could not open
> appstream://org.kde.kdeconnect.app" are entirely unrelated. For the former
> see https://bugs.kde.org/show_bug.cgi?id=462931

Ok so I followed that thread to it's conclusion and removing the check in the vendor directory checkbox does prevent the issue occurring, however (and this is an arch newbie question) does that not limit the content that discover can now provide me? 

if no, then I'm happy this is resolved. If yes then it's not really a perfect solution. Just curious