System: Debian sid (unstable) with XFCE 4.14. Telegram v.1.8.15. This issue only for Telegram on XFCE DE. I've tested the Telegram on KDE, Mate and LXQT: LMC open Telegram window and RMC open Telegram menu as expected. But on XFCE LMC open Telegram menu like RMC. Other applications (Skype (electron based), Viber (qt5), uget (GTK2) and deluge (GTK3)) are have not this issue. Additional information: appindicator (libappindicator3-1) has been purged deliberately: it does not help. Please fix this.
I have tested it with xfce4-statusnotifier-plugin and it does open Telegram's context menu on left click also.
More information: when I launch the Telegram with command "env XDG_CURRENT_DESKTOP=NONE telegram-desktop -startintray -- %u", LMC works as expected. I think that this bug has to be closed.
In that case the tray icon appears in the Notification Area (classic tray) instead, right?
I don't use "xfce4-statusnotifier-plugin", only "Notification Area" plugin and all tests have made for it. I understood that I made mistake: in product selector I did not find "Notification Area" plugin and I select "xfce4-indicator-plugin" (let assigner select proper product). For your information: - "Notification area" is the classical system tray for X11. It's based on the XEMBED protocol. Due to being X11-specific, it's considered obsolete by many progressive minds who think that Wayland is the future. - "Status notifier" implements the StatusNotifierHost part of the StatusNotifierItem specification. This mechanism is based on D-BUS, which is independent of the windowing system, so it's compatible with X11, Wayland etc.. So, perhaps Telegram switched to XEMBED protocol after export XDG_CURRENT_DESKTOP variable with NONE value.
I've made more tests. I've installed xfce4-statusnotifier-plugin, add it to XFCE panel and test Telegram with different XDG_CURRENT_DESKTOP variables: $ telegram-desktop proto: D-BUS, LMC act like RMC; $ env XDG_CURRENT_DESKTOP=NONE telegram-desktop proto: XEMBED, LMC act properly; $ env XDG_CURRENT_DESKTOP=KDE telegram-desktop proto: D-BUS, LMC act properly; $ env XDG_CURRENT_DESKTOP=GNOME telegram-desktop proto: D-BUS, LMC act like RMC. So, I almost completely sure, that it is not XFCE bug.