SUMMARY
No files match the filter when attempting to install new cursor theme, so they cannot be selected in the UI. This includes new and previously working files.

STEPS TO REPRODUCE
1. Open kcm_cursortheme
2. Click "Install From File..."
3. Browse to directory containing theme

OBSERVED RESULT
No files are shown to install

EXPECTED RESULT
Files are shown to install

SOFTWARE/OS VERSIONS
Kubuntu 21.04
Plasma: 5.21.4
Frameworks: 5.80.0
QT: 5.15.2
Kernel 5.11.0-17-generic x64

ADDITIONAL INFORMATION
Konsole output:
$) ~/.icons/SM: kcmshell5 kcm_cursortheme
Model size of -82 is less than 0
Model size of -10 is less than 0
kf.kio.widgets.kdirmodel: No node found for item that was just removed: QUrl("file:///home/niko/.Xauthority")
Model size of -82 is less than 0
Model size of -10 is less than 0

Sample theme file
($) ~/.icons/warcraft-3-cursors: cat index.theme
[Icon Theme]
Name=Sorely's Warcraft cursors

Attempting to set a new cursor theme results in the following error:
QDBusConnection: error: could not send signal to service "" path "//home/niko/.kde/share/config/kdeglobals" interface "org.kde.kconfig.notify" member "ConfigChanged": Invalid object path: //home/niko/.kde/share/config/kdeglobals

Please file a bug report on https://bugs.kde.org, the forum is the wrong place to report this

The forum rules state not to file a bug report without posting here first. Would you prefer I just file bugs directly in the future?

chefniko wrote:The forum rules state not to file a bug report without posting here first. Would you prefer I just file bugs directly in the future?

...
If you meant the sticky topic: that should probably be removed as it refers to the Plasma 5 port 8 years ago, not to stable releases of 2021.
In general, unless stated otherwise by a specific project: reproducible bugs should go to the bug tracker.

Understood, thank you for the clarification!

Bug filed: https://bugs.kde.org/show_bug.cgi?id=437225