I have to start this topic again, there is something wrong with the previous solution. My brave-browser-nightly was showing active on the brave-browser taskbar icon.
Someone on the Brave Team(?) suggested this fix:
sudo sed -i ‘/Actions=new-window;new-private-window;/ a StartupWMClass=brave-browser’ /usr/share/applications/brave-browser-nightly.desktop
It did in fact make the brave-browser-nightly active on its own taskbar icon, but it also makes brave-browser open up using the nightly config files --it starts nightly instead of brave-browser.
I fiddled around with these files and even the application files, but I can’t get this working properly. Somewhere, there is a mismatch with links. I compared all three browsers’ application files thru to the .desktop files and tried a number of things, but got a big fat Zero 0.