It’s the first time I have to arrange something for SATB choir and I chose the respective project template but there are no sounds. I found that the audio tracks are empty (i. e. no sounds assigned). I also don’t see the Olympus Choir library anywhere. Could it be the fact that the sounds were not automatically installed when I upgraded from earlier versions of Dorico? Will I have to download the entire 9GB sound library again to install the choir sounds? 
If you had Dorico 3 installed, then you should already have had the Olympus Choir Micro sounds installed on your computer, so they shouldn’t need to be reinstalled.
I don’t have Steinberg Download Assistant installed on this computer, but I believe you will find Olympus Choir Micro available for download under the VST Instruments / Sound content category (pardon me if I am not plucking precisely the correct category name out of my head), which you can download on its own.
Thanks, Daniel. Yeah, I had Dorico 3.1.10 before, if I remember correctly, and upgraded to version 3.5 a while ago and to version 3.5.12 just earlier today. If I open Steinberg Library Manager, Olympus Choir Micro is nowhere to be seen, only various variants of HALion Sonic, and HALion Symphonic Orchestra. And the newest VST library is called “Indian Drum Basics” which was installed on 3 December 2020, according to the info on the item. How could the choir library get lost or be forgotten?
Also – and I don’t know whether it has anything to do with this – strangely, since the latest update, Dorico is crashing sometimes if I try to access the instrument editor window in Play mode by pressing that ominous “e” button. I’m gonna send you a diagnostics report about that.