Es gibt zwei Möglichkeiten:

Deaktivierung auf system level Ebene durch eine config Datei

Whilst telemetry is disabled by default, a user can choose to enable it inside applications.

To force global disabling set

/etc/xdg/KDE/UserFeedback.conf

[UserFeedback]
Enabled=false

URL: https://userbase.kde.org/KDE_System_Administration/Kiosk/Keys#Telemetry

Dekativierung in Firewall

If that's still not enough, you can also add a firewall rule to block traffic
to telemetry.kde.org, or add an entry into your hosts file pointing to a local
IP address.