Blues-Rock is in 4/4 and every quarter has 3 subdivisions. This cannot be displayed in sample editor. There is no way to see whether a signal (e.g. guitar chord or drum hit) is in-time, because the sample editor raster always displays 4 subdivisions per quarter note.
Workaround: If you want to edit blues-rock, don’t use Cubase 10, use something more professional
I’m not sure if I understand what you are missing , but is it possible to set a 6/8 signature and then work in half - 3/4 to achieve what you request ?
There are many very popular rhythms like Blues, Blues-Rock, Swing (Jazz), Bembe (Afro) which are triplet based. I cannot understand how Cubase can maintain its “professional” marketing-image without support for these basic ryhthms. Any serious test in a magazin shoud point out “Cubase cannot handle triplet grooves”. I was really shocked when I discovered this after I bought the PRO license. Not talking about advanced stuff like 7/8 etc.
e.g. “All Blues” from Miles Davis, very popular, played on almost every Jam Session. Cannot be produced with Cubase PRO See example Studio Jams #52 - "All Blues" - YouTube