There are plenty of threads around the internet with this problem, not everyone is able to reproduce it, and probably "fixes" don't always work. In my case, I'm not even on KDE/plasma, even though I prefer KDE file managers and dialogs.
What I found that worked for me so far was from here:
https://forum.manjaro.org/t/dolphin-...-load/69134/11
Quote:
Originally Posted by b_quest
It’s because dolphin may call upower when starting and upower fails and causes
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