any plug-in for distortion by too-high gain

[steve]

There is a dB view, but it probably does not display in the way that you would expect.
The usual reaction when people accidentally switch to the dB view is "what's gone wrong with the track display?" because it is unfamiliar and not immediately obvious how to interpret what it is showing.

To switch to the dB view, click on the track name and select "Waveform (dB)".
To change back to the normal waveform view click on the track name and select "Waveform".

The dB track display does have some uses, and is correct despite first impressions, though most people find the normal display to be far more useful and intuitive.