Error with QT Library When Calling `PyPlot` Uisng `PyCall` on Windows

I'm running the demo code on the `README` file:

```
plt = pyimport("matplotlib.pyplot")
x = range(0;stop=2*pi,length=1000); y = sin.(3*x + 4*cos.(2*x));
plt.plot(x, y, color="red", linewidth=2.0, linestyle="--")
plt.show()
```

I get the following error:


Then the REPL just crashes.

Could it be a missing installation by `Conda` or something?
Using Julia 1.6 on Windows 10.

If I set:

```
mat = pyimport("matplotlib")
mat.use("TkAgg")
```

Then it works.

Use the README demo as the reproduction entry point on Julia 1.6 and Windows 10, then compare the default matplotlib backend with the reported TkAgg workaround. The issue is complete when the PyPlot demo no longer crashes in the default setup, or the required Windows/Conda configuration is clearly documented.

Written by the indexing model from the issue text.