I am just looking to confirm that it is not possible to add BillboardTextActor3D to viewer geometries. I have tried a few things, but as the warning stipulates:
The 'geometries' trait of a Viewer instance expected A data structure for rendering geometry in vtk.js consisting of points, verts (vertices), lines, polys (polygons), triangle strips, point data, and cell data.
Thanks
https://kitware.github.io/vtk-examples/site/Python/Visualization/BillboardTextActor3D/