Coherence mode for Linux has been abandoned due to the hardship of maintaining it's code for future releases of GNOME compared to the percentage of users using it. However, it has been abandoned and deprecated and no longer works with current versions.
However, you can reuse the source code of Crostini instead to add Coherence for macOS. https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ash/crostini/ I think contains the source, otherwise you need to do some searching of code to find the bridge. Also, we don't need that menu and dock and stuff of GNOME as it looks ugly, just use stalonetray's source to bridge the tray to macOS, and bridge menu context items to the macOS bar, and use a few Crostini bridges for stuff like files. After that, you are done.
However, you can reuse the source code of Crostini instead to add Coherence for macOS. https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ash/crostini/ I think contains the source, otherwise you need to do some searching of code to find the bridge. Also, we don't need that menu and dock and stuff of GNOME as it looks ugly, just use stalonetray's source to bridge the tray to macOS, and bridge menu context items to the macOS bar, and use a few Crostini bridges for stuff like files. After that, you are done.