Yes, he's right in a way : Cubase was first called Cubeat, then Cubit, but for some legal reasons they had to change the name and it was first released in 1989 as Cubase 1.0, for the Atari. So there's no reason that in 1990, the Mac version would be named Cubit ;-)
this page shows some early atari history
http://atarimusic.exxoshost.co.uk/index.php?option=com_content&view=article&id=245:history-of-cubase&catid=59:atari-music-software&Itemid=213you might be better off looking on the 68k mac forums site
https://68kmla.org/forums/macos9lives is more powerpc oriented... theres some 68k stuff here but im sure they would be more specialized in the early 90s + system 7 versions of apps
i would love to hear if u succeed in finding the original cubase for the macintosh plus + mac SE/30 machines!
re: the name change from cubit to cubeat to cubase.... it says it exists at the top of the page (FIRST POST on this page)
Cubase 1.0 Macintosh 1990 - Cubase 1.0 is released for the Apple Macintosh computers
so it must exist as "cubase 1.0" only its rare + vintage + hard to find probably
but.. imho u might aswell just use the cubase 2.5 version or even the cubase audio XT
these are the last pre-vst versions that were MIDI or MIDI/AUDIO with no Virtual VST technology
and as far as i know they were all 68k compatible?? maybe mactron could confirm that
heres a related post:
https://www.gearslutz.com/board/music-computers/802894-vintage-mac-i-couldnt-stop-myself.html