On Linux it's a bit simpler because a new instance is launched each time you click the launcher icon. So all you have to do is set the config to show the profile manager at each launch.

macOS (and OS X before it) is more work. The Finder will switch to the running instance if there is one, instead of launching a new one each time you click. I worked around that with an AppleScript (for the icon and double-clickability) that calls a shell script with the proper args.

It sounds sketchy when I describe it, and is clearly not an obvious option for most people, but it has worked perfectly and invisibly for years.