I just downloaded with download assistent Elements 3 with HS SE.
Asked for an Activation number for a trial version and got one.
Installed both packages (Dorico and HSSE).
Started Dorico:
Message: Enter Activation!
Done.
Says that I have know the Trial Version 2.2.
???
Restarting…
Message: Enter Activation!
Looking in soft licenser I see the license for Dorico 2.2 Trial.
2.2 ?? or 3 ?? Running is nothing…! 
Protected to death… 
The Dorico Elements 3 (and indeed Dorico Pro 3) trials are not yet available. They will be available in the next two to three weeks.
So what did I download ??? 
Would be a nice job for the download assistant to prevent such problems.
Edit:
But it’s only a license problem? Or is the trial version another installer package?
I can use this installation with my USB Stick but then it’s the Pro version.
I want to check the Elements version. Can I reduce it to elements just on my MBP?
I want to check it because later I would have to purchase the Elements version to run it without dongle.
You very likely downloaded Dorico Elements 3, which we have to make available in Steinberg Download Assistant for people who have, you know, bought it.
Again (because I was too slow in my edits 
):
So I downloaded Elements. On my stick is Pro3.
Can I restrict the started Pro3 version on my MBP to Elements by some configuration?
If yes, I do not need any trial licenses. To test it first with dongle would be sufficient.
@pianoleo Thanks.
…for people who have, you know, bought it
I bought 1, 2 and finally, you know, as a guitarist bought 3 and I even can use it
Congrats and have fun!