gradient tool bug & default open app

After I updated the latest version 23.0, I have a problem choosing and modifying the gradients.
I tried to switch to another tab, then go back to the gradient tab, tried to reload my workspace, but still, it is no working properly.
I cannot choose the color dot, cannot select the exact color anchor in the gradient.
The only way to fix it is to resize the whole application, (click
) then expand the app to full size again.
This caused me a lot of trouble... a great lot. Please fix it.....
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here's another question, why is it all my illustrator files are labeled to be opened by XD by default?
I reset the default in windows right click (screenshot below)

still it is opened in XD by default.......................all the time.
it's like i cannot change the default app to open the file!
