Adding a custom tray icon for Electron applications

[Bingo90]

Hello, I'm trying to figure out how to add a custom icon for electron applications. I tried both Discord and Cider (the Apple Music app), both displayed "chrome_status_icon_1" when inspected with Looking Glass. This seems to make it impossible to set individual icons for them. Additionally, setting an icon for "chrome_status_icon_1" doesn't even work. Is there a way to get a different, working ID or are electron applications not supported?

EDIT:

After a restarting Discord, the icon did change - but not to the one I chose, but the three dots icon that seems to appear when an icon doesn't work.