The old 256x256 pixel JPG icon image is now PNG and 2560x2560 pixels.
Electron 3 has a bug, that the tray left click does not work, it behaves as right click. So you know this bug is persistent. You are open to use the previous release, which is just on Electron 2 and works.
Electron 2:
https://github.com/patrikx3/onenote/releases/tag/2018.9.5-5