PysimpleGui Control update

Dear Forum

As normal in PysimpleGui, e get event ans values using

Event,Values =

inside the while loop.
All work ok.

Now I try to modify the value of a control ,not via mouse, but in a external Thread,that periodically change a variable, and update the control.
For example, I modify the checkbox property, from false to true :
#identify the control via Key
CHKbox =MyWindow[‘CHK_TSCMask’]

#Modify the value to true
CHKbox.update (value=True)

Now, i want reads the -true- value i set before:
Is_Checked =Values[‘CHK_TSCMask’]

But this dont work…I get False.

I read the correc value, only if change the property via Mouse,… not via update().

Need Help