where to report a bug about kde applications 17.07.90 ?
Most people that assume that they may struck a bug discuss it here in the forums to see if others think the same (often an easy solution comes forward instead). Also when one in such a thread publishes a link to the report, other people can add information and confirmation to the report which might be helpful to get a bug resolved.
But there is of course https://en.opensuse.org/openSUSE:Submitting_bug_reports
And when you think it is pure KDE, independent of the distribution https://bugs.kde.org/