TextBox(ax=plt.gca(), label='radius', initial='2')

You need to assign this to something so it doesn't get garbage collected, as noted in its docs.

The bug persists even if we keep a reference to the TextBox.

Namely, the following code produce a TextBox that is non-editable on MaxOSX backend (yet, it is ok on TK backend):

%matplotlib osx
import matplotlib.pyplot as plt
from matplotlib.widgets import TextBox
h = TextBox(ax=plt.gca(), label='radius', initial='2')

I'm able to edit the textbox on current main, so I think this has likely been fixed in a more recent version. 2.x is quite an old version of Matplotlib now and there has been a lot of work on the macosx backend since then.

edit: This fails on 3.5.x, but is working on 3.6.x so the fix is only in the most recent release series.

fantastic - thanks !
btw: the original issue was raised for Ver 3.5.3 (2.5.3 was a typo - sorry)