I was trying to set flags for launching Signal desktop to line up in both the 'App Menu' (which can be edited via the 'Main Menu' app) - which I believe is also 'brisk-menu' - as well as the Plank dock.
Long story short I had started with Plank and set it up to execute via a file in my home folder ~/.local/share/applications/signal-desktop.desktop which had the correct flags.
When I looked at the settings in 'Main Menu' (which looked like the app for editing the menu) the flags looked correct, however when I launched signal-desktop the flags were not set correctly. It seemed to launch via /usr/share/applications/signal-desktop.desktop.
As an experiment, I discarded the changes to Plank and deleted the signal-desktop item in 'Main Menu'. However, now I'm not sure how to get it back in the app menu.
I tried re-installing Signal and the menu applet, but it doesn't come up; I couldn't find documentation to help me locate the settings for the main menu. I thought it was find the /usr/share/applications/signal-desktop.desktop file and create a new item, but it has not.
Any hints? Where are the files for the main menu?