Since the introduction of automatic day/night theme switching (https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/5574) allowing creating global theme from current configuration as a user would be a great addition to make the above mentioned feature more flexible. It could also be useful to save desktop layout as mentioned this report : https://bugs.kde.org/show_bug.cgi?id=412906
See lookandfeelexplorer in plasma-sdk
That's a developer tool with a pretty junky UX. There's already a feature request for a better UX that's integrated with the KCM. *** This bug has been marked as a duplicate of bug 412906 ***