We’re well into 2026 and apparently this is still a problem. I just tried KDE since I kept reading about how customizable it is. The first thing I do is move the taskbar to the left since I have an ultra-widescreen monitor. This made the time and date look really bad, and honestly this immediately made me less optimistic. If the most simple and fundamental visuals are handled poorly, what other surprises await? But surely it could be customized so I can just have the date as MM/YY and time as HH:SS, with the time as 12 hour without am/pm. As it turns out, the date format can be set as desired, but for some baffling reason the time format cannot.
I did some research and didn’t find a good solution. At that point I just reinstalled with Cinnamon. Having to struggle right away with (as seen here) an issue that has been unresolved for years is just not worth the effort. I might try KDE on a different computer where I don’t have an ultra-wide monitor, but it would be nice if the developers would make a simple change so the date and time formatting are handled in a consistent manner.