Something I tried to address with [1] but it needs further investigation, or a fix/workaround in Task Manager plasmoid.

[1] https://phabricator.kde.org/D16087

*** Bug 402663 has been marked as a duplicate of this bug. ***

I can reproduce in Manjaro with Plasma 5.14.4, Frameworks 5.52, Qt 5.11.2. Note I'm using the *Breath* icons, which I assume inherits the Breeze icons.

* https://github.com/KDE/plasma-desktop/blame/master/applets/taskmanager/package/contents/ui/ContextMenu.qml#L101
* https://github.com/KDE/plasma-desktop/blame/master/applets/taskmanager/plugin/backend.cpp#L286

Here's the KFileItem::iconName() code path:
* https://github.com/KDE/kio/blame/master/src/core/kfileitem.cpp#L893
* https://github.com/KDE/kio/blame/master/src/core/kfileitem.cpp#L1492


-----
If I add a few `qDebug()` statements, it seems all the "Recent Doc" icons are "application-octet-stream".

        qDebug() << "url:" << url;
        qDebug() << "   scheme:" << url.scheme();
        qDebug() << "   isLocal:" << url.isLocalFile();
        qDebug() << "   isDir:" << fileItem.isDir();
        qDebug() << "   icon:" << fileItem.iconName();

url: QUrl("/home/chris/Pictures/Screenshots")
   scheme: ""
   isLocal: false
   isDir: false
   icon: "application-octet-stream"

I tried setting the scheme to "file" when it's empty. Which fixed `url.isLocalFile()` but did not fix `KFileItem::isDir()`.

        if (url.scheme() == QStringLiteral("")) {
            url.setScheme("file");
        }

url: QUrl("file:///home/chris/Pictures/Screenshots")
   scheme: "file"
   isLocal: true
   isDir: false
   icon: "application-octet-stream"

This still occurs in the following software versions with the Breeze theme.

KDE Plasma Version: 5.15.1
KDE Frameworks Version: 5.55.0
Qt Version: 5.12.1

*** Bug 408337 has been marked as a duplicate of this bug. ***

There are two possible patches that could fix this:
- https://phabricator.kde.org/D16087
- https://phabricator.kde.org/D22005

In my case (Plasma 5.16.2 on Kubuntu 19.04) both folders and Kate text files show the unknown icon in recent documents. This all worked fine for me in Plasma 5.15.4 (also tested on Kubuntu live iso).

Created attachment 121732 [details]
unknown icon in "History" tab of kickoff

Related: "History" tab of kickoff also shows unknown icon for recent documents.

Operating System: KDE neon Unstable Edition
KDE Plasma Version: 5.16.80
KDE Frameworks Version: 5.61.0
Qt Version: 5.12.3

Méven, could this be a problem in KActivities?

Nate, not likely, KActivities only stores file paths, the view and icon are the responsibility of the client, here the kickoff plasmoid.

https://phabricator.kde.org/D22005 Seems to me the way to go

About the second screenshot added in :

 Patrick Silva 2019-07-25 18:02:15 UTC

Created attachment 121732 [details]
unknown icon in "History" tab of kickoff

Related: "History" tab of kickoff also shows unknown icon for recent documents.

Operating System: KDE neon Unstable Edition
KDE Plasma Version: 5.16.80
KDE Frameworks Version: 5.61.0
Qt Version: 5.12.3

Could you Patrick Silva please file a separate bug next time.

This is a bug introduced in :
https://phabricator.kde.org/D19784#502503
The comment pointed diagnoses the issue and suggest a path to fixing.

I bet this is pretty much the same thing as I tried to address in https://phabricator.kde.org/D22005

@broulik Your patch addresses an older bug in task manager, and although the new one has a similar effect, it is caused a missing mimetype check rather an incorrect url passed. See https://phabricator.kde.org/D19784#502503

(In reply to Méven Car from comment #11)> 
> Could you Patrick Silva please file a separate bug next time.
> 
> This is a bug introduced in :
> https://phabricator.kde.org/D19784#502503
> The comment pointed diagnoses the issue and suggest a path to fixing.
reported as bug 410300

*** Bug 410300 has been marked as a duplicate of this bug. ***

Patch proposal: https://phabricator.kde.org/D23198

*** Bug 412312 has been marked as a duplicate of this bug. ***

Hi,

It's still present in Opensuse Tumbleweed. 
-Kde applications 19.12
-Plasma 5.17.4
-Kde Frameworks 5.64

Alternative to D23198: https://phabricator.kde.org/D26407

Half fixed with https://phabricator.kde.org/D26580

Hopefully the rest will be fixed soon with https://phabricator.kde.org/D26407

There's a patch that fixes this: https://phabricator.kde.org/D26407

A possibly relevant merge request was started @ https://invent.kde.org/frameworks/kio/-/merge_requests/174

*** Bug 435366 has been marked as a duplicate of this bug. ***

A possibly relevant merge request was started @ https://invent.kde.org/frameworks/kio/-/merge_requests/780

A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/1507

Git commit 02d6d0a4090094437bc5ff334d124e9cf3b8b70e by Nate Graham, on behalf of Méven Car.
Committed on 14/03/2022 at 13:38.
Pushed by ngraham into branch 'master'.

RecentUsageModel: propagate mimeType to KFileItem ctor
FIXED-IN: 5.25

Best used in conjunction with with
https://invent.kde.org/frameworks/kio/-/merge_requests/780 which will
allow kicker recentUsageModel not to make any stat call but solely
base its iconName based on passed mimetype, allowing to act as if
KFileItem::SkipMimeTypeFromContent was set.

M  +1    -1    applets/kicker/plugin/actionlist.cpp
M  +9    -4    applets/kicker/plugin/recentusagemodel.cpp
M  +1    -1    applets/kicker/plugin/recentusagemodel.h

https://invent.kde.org/plasma/plasma-workspace/commit/02d6d0a4090094437bc5ff334d124e9cf3b8b70e