The problem in encountered in current Google Collab version. If I use ipympl the easiest way - the code worked about two months ago:

!pip install ipympl
from google.colab import output
output.enable_custom_widget_manager()

%matplotlib ipympl

I get an Error message:

Key backend: 'module://ipympl.backend_nbagg' is not a valid value for backend; supported values are ['gtk3agg', 'gtk3cairo', 'gtk4agg', 'gtk4cairo', 'macosx', 'nbagg', 'notebook', 'qtagg', 'qtcairo', 'qt5agg', 'qt5cairo', 'tkagg', 'tkcairo', 'webagg', 'wx', 'wxagg', 'wxcairo', 'agg', 'cairo', 'pdf', 'pgf', 'ps', 'svg', 'template', 'module://ipykernel.pylab.backend_inline', 'inline']

However, If I do

%matplotlib --list

I get:

Available matplotlib backends: ['tk', 'gtk', 'gtk3', 'gtk4', 'wx', 'qt4', 'qt5', 'qt6', 'qt', 'osx', 'nbagg', 'notebook', 'agg', 'svg', 'pdf', 'ps', 'inline', 'ipympl', 'widget']