According to your diagnostics report, your path to Dorico 3.1 is /Applications/Dorico\ 3.1.app
therefore I wonder that it can’t find that path. There was a typo in the path to Altiverb, but the parsing did not even get to there and bailed out already on the Dorico path.
Please try again with this command:
/Applications/Dorico\ 3.1.app/Contents/Applications/VSTAudioEngine3.app/Contents/Components/VSTPlugManager.bundle/Contents/Resources/vst2xscanner -p /Library/Audio/Plug-Ins/VST/Audio\ Ease/Altiverb\ 7.vst
I think this is correct.
If it still does not work, go the long way. First do
several times until you are in the root directory, then
cd Dorico\ 3.1.app
and so on, until you are in the Resources directory, then issue the command
./vst2xscanner -p /Library/Audio/Plug-Ins/VST/Audio\ Ease/Altiverb\ 7.vst
Does that work?