Is there some way to visualize data from .vti file as a volume not using ParaView, but using just python?
And if there is, is there a way to connect it with some .stl file?
The ideal solution would be to have the same output as from ParaView but using only python.
ParaView has a python wrapping https://docs.paraview.org/en/latest/UsersGuide/introduction.html#getting-started-with-pvpython.
Your file is a VTK file, so you can also use the VTK python module https://pypi.org/project/vtk/.
Also you can use pyvista, a user friendly wrapper around VTK https://docs.pyvista.org/version/stable/index.html