If I select a given folder to have its contents shown in the message list, then go to Settings -> Appearance -> Layout and change the Folder List option from long to short (or vice-versa), the messages in the message list disappear. I need to switch to another folder and the back to the original one to see its contents again.
I confirm it
Git commit b269da73b1e5c6d6182ef189a5be959c2e64d826 by Laurent Montel. Committed on 16/03/2023 at 06:16. Pushed by mlaurent into branch 'release/23.04'. Fix bug 467291: Switching Folder List layout causes messages in message list to disappear FIXED-IN: 5.23.0 M +1 -0 src/kmmainwidget.cpp https://invent.kde.org/pim/kmail/commit/b269da73b1e5c6d6182ef189a5be959c2e64d826