@Sand1024
As a result of your advice I now have the Icon for the "Snap Middle Manual" icon.
In answer to your question, I'm a CAD novice so I turned to the LibreCAD manual at
https://docs.librecad.org/en/2.2.0_a/Although the Snap Middle Manual icon appears in the LibreCAD window the manual doesn't even mention the Snap Middle Manual tool. I was writing a short Aide-mémoire about it for myself.
A search of everything at
https://docs.librecad.org/ failed to find any reference to "Snap Middle Manual".
Do you have any pointers to information about that tool?
Thanks for your helpful advice.