Do you want 0 dB peak amplitude?
Because “noise” is random, the peak value is not really a reliable measure. More usually RMS level is used for this type of thing, but a lot lower than 0 dB.
The default 0.8 will generate a peak level of “about” +/- 0.8 linear (not exact, because of the random nature).
0.8 linear is -1.9382 dB relative to full scale.
Generating to 1.0 will give a peak level of about +/- 1.0 linear (0 dB).
To get a specific RMS level, generate some noise (default 0.8 will do), then use this plug-in to amplify to the required RMS level. https://forum.audacityteam.org/t/rms-normalize/40902/1 Read the full post for details about the effect and installation instructions.