As you found in the documentation, vtk-osmesa is gone and osmesa is now part of vtk wheel. We are still in the process of publishing stable wheels for 9.4 on pypi. You can get release candidates from wheels.vtk.org.
pip install vtk==9.4.0rc2 --extra-index https://wheels.vtk.org
About this,
It indicates that the trame docker setup needs to update their dependencies to replace vtk-osmesa with vtk. I think this is the file - trame/examples/deploy/docker/VtkRendering/setup/requirements.txt at master · Kitware/trame · GitHub. I would guess someone will get to it after VTK 9.4 is published on pypi. @Sebastien_Jourdain
A more recent update about osmesa and EGL in vtk wheels is here Status Update: Runtime OpenGL render window selection in VTK