So far as I can tell the default tempo is hard-coded at 120 bpm. We cannot change this default, or if we can I have not found evidence of this using forum search and manual search.
I would like the ability to set the default for ourselves. 120 bpm is invariably too fast for the vast majority of the work I do. If I could I would set the default to 90 or 100.
I grant that tempo varies by composition and personal preference, but I figure there might be others who would like the default tempo to be within shouting distance of their comfort zone. Hopefully this would require no more than adding a setting in Preferences or Playback Options.