matplotlib, no plot when using Figure

[ajvperth]

Hello,
as I am breaking by brains about this, I hope you can give me a suggestion.
I work on Linux / openSUSE 15.3 and python 3.9.4 in a virtual console.
I can not understand why this is not providing a plot output

import matplotlib.pyplot as plt
from matplotlib.figure   import Figure

fig = Figure(figsize=(5, 4), dpi=100)           # Create a in memory figure
ax  = fig.add_subplot(111)                      # Create a axes in fig
ax.plot([1, 2, 3, 4], [1, 4, 2, 3])
plt.show()                                      # Show in X

and this does

fig, ax = plt.subplots()               
ax.plot([1, 2, 3, 4], [1, 4, 2, 3])
plt.show() 

Thanks, Anthony