I had Google Chrome as default E-Mail client, this setting was set by Chrome itself. Now I want to send E-Mail via KMail, so I set in Default Applications to "KMail as default preferred email client", but if I click "mailto:" links in Chromium (i have many browsers installed) it will be still opened Google Chrome. KDE Neon, Plasma 5.13.3
Seems like a bug in Chrome; it takes over the setting and overrides what's set in System Settings. Please report this to the Chromium devs.