I'm trying to find a way to take a figure previously created, and show it inside a widget, without losing interactivity.
Here's a short version of my approach (which may not be the right one):

fig = plt.figure() # previously created figure
out = widgets.Output()
with out:
    display(fig)
# other things happening
display(widgets.HBox([fig.canvas, some_other_fig]))

If I first create a figure in the notebook outside of an Output widget, and then wish to include it later inside something like an HBox next to a second figure, I seem to lose interactivity with the figure (including the nice ipympl zoom interface).

Here is a nbviewer view of a MWE notebook I created, download it top right on the window. It's best if one downloads it and runs it since the first figure appears buggy in the nbviewer.

Additionally, and I might create a new issue for this - if I call fig1 at the end of the notebook, I get an unexpected error. Here I'd expect the regular figure to be shown. The error is AttributeError: 'NoneType' object has no attribute '_send_event'.