Using my latest keymap I now get the context menu when the AV button is pressed.
The showing of the weather screen has always been a problem even under Kodi 18. There I was using the OSMC supplied keymap. It was only on reading this old post [RESOLVED] Disable a specific TV remote control key that I decided to try and build my own keymap, ohh and because Kodi 19 must have changed the keymap and some of the buttons that did work under Kodi 18 didn’t after the Kodi 19 install.