Hi Jacqueline,
What issue are you running into?
The plot_cnv() method allows you to manually plot the figure that you would usually get from infercnv and has a number of configuration options. Since you have a high number of cells, I would suggest using the dynamic_resize option so that the figure has more height and so cells are less compressed.
Another option is to use the plot_per_group() method which allows each annotation group (reference and/or observations) to be plotted on a separate figure where only the bottom heatmap space is used. This method also has options to sample cells if there are more than a given number, and control what frequency to sample at. You can also decide to save the internally generated infercnv objects for each annotation group to use them with plot_cnv() if you want to use specific settings.
Alternatively, you can use the sample_object() method to downsample your results and then plot them with plot_cnv().
Regards,
Christophe.