I had R2018b version and when I opened the app designer, a white window was showing up. Actually, the page was behind the white page because the names of the icons showed up with the hand form of the mouse. Then I upgraded to R2020b version but now I have the same problem. Only change is the window poping up is no more white but black.
I've already tried to create new R2018b and R2020b folders by the way.
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