I noticed multiple bugs in KDE System Settings. Not sure if they are KDE-related, Arch-related or antergos-related. But here’s the list:
Installed Evolution and uninstalled it shortly. Since then, clicking any mailto: link displays a pop-up error - Evolution not found. And then some other popup about KIO or KIOExec error. Of course, tried to change default mail client using Default Applications > Email Client tab, but no effect. No matter if I choose option “Use Kmail” or “Use a different email client” and enter it here, the same errors about Evolution missing were displayed all the time. The only way I could fix it - locate mimetypes.list file and manually edit it. There was an entry for x-scheme-handler/mailto set to Evolution, which I changed to claws-mail.desktop and it started working fine. For the record, my current setting in System Settings > Default Applications is set to KMail (which isn’t even installed), but Claws Mail is opened after clicking any mailto link. In other words, KDE settings have no effect.
Similar issue for Default Applications > Web Browser. I selected option “in the following application” (and selected Vivaldi) for open http and https URLs setting, but it had no effect. Every time I clicked a link in some desktop app (email client, text editor, etc.) it opened BlueFish text editor which then displayed the source code of requested page. I realized that as soon as System Settings is closed, open http and https URLs setting reverts back to “in an application based on the contents of URL” and for some reason it executed BlueFish. I could partially fix it by choosing “with the following command” option and entering vivaldi-stable. Interesting, once System Settings is closed, selected option automatically changes to “in the following application” and Vivaldi is displayed then. Well, at least URLs are now opened with Vivaldi…
Account Details > User Manager tab can’t enable auto login. I select my user (I’m the only user), select Log in automatically and password prompt appears. I enter my password and Log in automatically is checked. Once I close System Settings (or even jump to other tab in System Settings), the box becomes unchecked and auto login never works.