In VLC 3.0.19 (Linux) the amplification goes up to '200%' (note that the UI icon and font don't exceed '125%', the on-screen display does). With my current audio hardware there's no need to use the feature.
Pressing the up arrow ↑ increases the volume by 5% (in the mpv media player I've developed a muscle memory to skip forward with the key). I haven't been able to unbind the arrow keys, in the configuration file ~/.config/vlc/vlcrc
the functionality is now mapped to nothing:
# Volume up (string)
#global-key-vol-up=
# Volume up (string)
key-vol-up=
# Volume down (string)
#global-key-vol-down=
# Volume down (string)
key-vol-down=
I was able to disable the mouse wheel, which also controls the volume by default.
Additionally disabling 'remember the audio volume' option doesn't appear to work — the level of volume is saved and persists between media files.