Overwritemode don't work in QTextEdit / QTextBrowser

[seediq]

Hello, i'm currentlly using the PySide2 package. And found that the overwritemode won't work in my Code. Here is what I wrote:
I used Qt-Creator to design my GUI and my settings for the QTextBrowser looks like that:

menu1, menu2, menu3 are just three PushButtons, I clicked them one by one and got the following output:

And print output is True. The old text is not replaced.

I am new to Qt and can anyone please help me out? What am I missing?