Using plt.interactive(False) or plt.ioff() in Jupyter (Lab and classic notebook) does not seem to prevent automatic figure generation, unless the magic %matplotlib inline in run first, even though the inline backend is the default.

Example

import matplotlib.pyplot as plt

plt.ioff()

fig, ax = plt.subplots()
a = 0

The figure still appears automatically under the cell.

Note that

Explicitly running %matplotlib inline blocks figure creation (even though inline is the default activated backend in Jupyter):

Originally posted in matplotlib/matplotlib#23766