SUMMARY: The default calendar experience on KDE is horrible, especially the calendar applet/plasmoid, it's plain ugly and non-functional. One possible solution is to do what GNOME does: Ask Google/Microsoft account info at first run and integrate it with the calendar applet. But still, the applet remains ugly. There's an excellent plasma widget called event calendar(https://store.kde.org/p/998901/). Which has cool features(weather, timer), is better looking, integrates with google flawlessly( to a degree) and is generally used by everyone using KDE. So why not go ahead and make that the default( or incorporate it's design and functionalities into the default widget)? Why have tons of users download a widget as 'default'?
Created attachment 144401 [details] Event calendar widget
Created attachment 144402 [details] KDE calendar applet
If you prefer the Event Calendar applet, you're welcome to use it. "non-functional" is clearly incorrect; the existing calendar is quite functional. "ugly" is a judgment call. From my perspective, the Event Calendar applet looks much worse as it has weird margins and paddings, tons of stuff crammed together really close together, and no logical separators (whitespace, lines or different background colors) to distinguish different elements of the applet. And it has a weird floating refresh button on top of a scrollable view. So I feel quite confident in saying that the default calendar applet isn't uglier than Event Calendar. If you have specific actionable bug reports or suggestions for improvement, feel free to open new, focused bug reports about them. You may want to read through https://community.kde.org/Get_Involved/Issue_Reporting first.