Since Plasma Desktop 5.18, notifications widget is broken unless you manually install graphics/kf5-kquickcharts.
I think it should be included as a direct dependency
Good catch, I'll fix it shortly.
(In reply to Tobias C. Berner from comment #1)
Thank you :)
A commit references this bug:
Date: Sun Feb 16 19:00:38 UTC 2020
New revision: 526313
Add missing run-depends to x11/plasma5-plasma-desktop
(Checked upstream, it is a required-optional runtime dependency)
Reported by: Patricio Vilar