Good morning, and here now what to do:
With Spotlight search have a look for Terminal.app and open.
In the Terminal window copy and paste one by one the following two lines
sudo chown sophia:staff /Library/Application\ Support/Steinberg/Content/HALion/VST\ Sound/*
sudo chown -R sophia:staff /Library/Application\ Support/Steinberg/Content/VST\ Sound/*
After copying and pasting one line, press the enter/return key. You will get prompted for your password. Type it in and then hit enter or return once more again.
Most likely you won’t get asked again for the password after pasting the second line. The computer just remembered it from before.
That should be it. Relaunch Dorico and see how it goes.