A little report here:
While listening to a track on Logic Pro through headphones connected to an RME Fireface 400 soundcard, I opened Dorico 2.
While Dorico was showing the splash screen the volume on the soundcard output suddenly jumped to full. Luckily the music itself wasn’t loud so I think my hearing is still all there!
I turned the output back down, and proceeded to open a new project in Dorico while the track on Logic Pro continued playing.
Then the same thing happened just as the new project opened.
I checked this again with Logic Pro closed and it behaved the same way: the volume jumped up to full both during the spalsh screen and during the opening of a new project.