now in a number of plots we have MEG topos that appear circular instead of following the helmet shape.

See for example:

https://mne.tools/dev/_images/sphx_glr_plot_20_visualize_epochs_008.png

in

https://mne.tools/dev/auto_tutorials/epochs/plot_20_visualize_epochs.html#sphx-glr-auto-tutorials-epochs-plot-20-visualize-epochs-py

I don't know if it's a problem of defaults but I also see around me a lot of people showing me MEG topos with circular shapes and I feel it should not happen.