See this example that uses hemi='split', all captured PyVista images are duplicated:

https://mne.tools/dev/auto_examples/visualization/plot_publication_figure.html#sphx-glr-auto-examples-visualization-plot-publication-figure-py

Moreover, once brain.close() is called, it should make sure no figures are generated (as they have been closed for that snippet). Compare the above to what used to be produced with mayavi produced (one pair of images rather than four pairs):

https://mne.tools/stable/auto_examples/visualization/plot_publication_figure.html#sphx-glr-auto-examples-visualization-plot-publication-figure-py

cc @GuillaumeFavelier can you look into it?