This is a pretty minor bug in the Linux build, all told.
Sometimes, when I launch Spinnortality with certain other apps' windows open, Spinnortality will appear in the Cinnamon taskbar as a second window of those apps.
So far, this has happened with Freetube and Whatsie. I'm running both of those via Flatpak, if that makes a difference?
I'm on Linux Mint 21.3.