Bug report

Bug summary

After #16818, with the TkAgg backend, configure subplots window can't be closed and the sliders do not respond to input. The window close issue is straightforward to understand: the button response calls Gcf.destroy but the figure is intentionally not registered, so the FigureManagerTk.destory is never called. I suspect (but have not confirmed) that the slider events are being lost due to the new figure manager making a new tkinter.Tk instance here. [EDIT: NOPE, see comment]

CC @anntzer

Code for reproduction

import matplotlib
import matplotlib.pyplot as plt

matplotlib.use("TkAgg")
plt.plot([1,2,3],[1,2,5])
#  if not interactive
plt.show()
# click Configure Subplots

Actual outcome

interactive Tk window but sliders don't work and close window button is not responsive

Expected outcome

previous behavior

Matplotlib version

• Operating system: Win10
• Matplotlib version: master
• Matplotlib backend (print(matplotlib.get_backend())): TkAgg
• Python version: 3.8.5
• Jupyter version (if applicable):
• Other libraries: