We are already on the VTK specific Discourse, and so specifying VTK Support rather than just support feels overly repetitive. Even more so when using Discourse in mailing list mode and seeing posts tagged [VTK][VTK Support]. Consider simplifying to Support.
The thought process was to distinguish among VTK the C++ library and and other VTK-related things like VTKWeb, vtk.js, etc., but your point about redundancy in the email subject lines is taken. One option might be to change it to “C++ Library”, but that doesn’t feel right.
How about instead of VTK Support we change it to Help? Help is maybe clearer.
Support or Help seem equally good to me, adding in VTK before those words doesn’t add any useful information as far as I can tell - I am already on the VTK Discourse. C++ Support, Web Support, etc would make it clearer you wanted to separate Support/Help along the lines of language. It was just a suggestion, if you prefer to be repetitive I will get used to it. In general we only need telling once that this is VTK, more than that will tend to feel repetitive…
I have dropped VTK from the support category. May your inboxes forever be free of redundant "VTK"s.