Time Sig: 3/4
Seems like the Factory default should work in 3/4.
Go to notation options>beams and check the very first option there.
[3]/4 works but might have unwanted consequences.
Jesper
Since it’s a very common notation, I agree that it would deserve a Notation Option. I think it has already been discussed here.
I understand it is discouraged, because it is confused with 6/8.
Yes. Western notation rules taught in basic theory and composition classes would have the first 8th/quaver not beamed to the last two. Adjusting the time signature as previously described by @John_Lilja would probably be the correct way to have all three beam together.
That’s not to say that modern music cannot break the rules but just that Dorico probably will not help with that minor form of anarchy (not judging). The only other option is to manually beam them together by selecting all, right clicking with the mouse, Beaming->Beam Together.
Modern music and Schubert! 
— Jim
Schubert - what a rascal!
I still wanted to quickly double‑check that I wasn’t saying something incorrect, but everything I’ve seen confirms that beaming the last three eighths together in a 3/4 is really frequent, not to say the norm, at least from Bach until the early XXth century.
Some examples
Bach (Bärenreiter)
Beethoven (Henle)
Brahms (Henle)
Brahms (Peters)
Brahms (Simrock)
Chopin (Paderewski)
Debussy (Durand)
Mahler (UE)
Mozart (Bärenreiter)
Manuscript of the same:
Prokofiev (Boosey & Hawkes)
Ravel (Durand)
Schubert (Bärenreiter)
Schumann (Peters)
Schönberg (UE)
Johann Strauss (Breitkopf)
Stravinsky (Dover)
So, yes (while I understand the objections), I vote for a Notation Option
(btw this is already the way 6/4 is displayed by default)
I can’t agree more.
I think it is absolutely fascinating that various publishing houses contradict what we were taught back in the late 70s and early 80s. To me, it simply means that there are more ways than one to “correctly” notate many patterns and, in particular, the one in question here. Great examples!