Chromium and Firefox’s chrome now support tab groups, and the same has been suggested for VS Code, to significant support:
Similarly, can I group multiple applications in the Task Manager plasmoid? I presume not, so if not, does a feature request exist for it, or an alternative plasmoid?
I’m aware that I am able to have them automatically group per application:
You might be able to manually approximate is using multiple instances of the Task Manager or even Quick Launch widget separated by fixed-width spacers or something, but that’s going to be left as an exercise for the reader.