Just installed merkuro (26.04.0-1) on my pc (using kde plasma 6.6.4) and when installing merkuro only the calender and contacts are added to the application launcher i needed to start the merkuro-mail through the terminal.
Would be awesome if merkuro-mail was not hidden by default in the application launcher
Upstream hides it from the menu purposely, not sure why. You can change it by copying /usr/share/applications/org.kde.merkuro.mail.desktop to ~/.local/share/applications/, then remove the NoDisplay=true line at the bottom.
Did the change in the application launcher settings to have it unhidden, and then read that the merkuro-mail is still in beta so that might explain it.
The client only support reading mail and not sending it.