When right-clicking on a mail, a context menu appears. When selecting "Move message to " or "Copy message to ..." (translated from German), that submenu instantly disappears, so messages cannot be moved or copied using the context menu. Dragging and dropping into a folder or a favorite folder on the left works. This is a known problem on Plasma 6 when using wayland and can be worked around by starting kmail using QT_QPA_PLATFORM=xcb /usr/bin/kmail or starting kontact using QT_QPA_PLATFORM=xcb /usr/bin/kontact Upstream bug report: https://bugs.kde.org/show_bug.cgi?id=485661