mlab.init_notebook() fails with AttributeError: module 'base64' has no attribute 'encodestring'

Using `mayavi`, following [https://docs.enthought.com/mayavi/mayavi/tips.html](https://docs.enthought.com/mayavi/mayavi/tips.html) is broken for me. I.e., initializing the `ipy` backend fails with

`AttributeError: module 'base64' has no attribute 'encodestring'`

Using the `png` backend works. The `x3d` only shows a grey canvas without content.

I'm running an Anaconda environment. Some (hopefully) relevant info about the packages in it:

python 3.9.4
mayavi 4.7.2 (build py39h3a0f4c8_4, channel conda-forge)
ipyevents 0.8.2
ipywidgets 7.6.3
jupyter 1.0.0
vtk 9.0.1
pyqt 5.9.2
qt 5.9.7
qtpy 1.9.0

I'll supply any other info needed happily.

The system I'm running on is a 64bit linux, opensuse leap 15.x, with qt 5.9.7. I'm rather sure, it is not an operating system issue, since with older python versions, i.e. python 3.7.x I had no issues of this sort on the same machine.