Thanks Joerg
Having now examined the files in the VSTSounds “common” location on the Mac which you pointed me to. (/Library/Application Support/Steinberg/Content/VST Sound)
I notice it contained Alias links to private files for Cubase 11 - FCP_SMT_008_Cubase.vstsound. as well as to Cubase 12 - (SMT_001, SMT_002, SMT_004,SMT_005 and SMT_009).
Despite there being a separate folder for Halion there were also some HSSE links along with the new VSTSounds from Cubase 13 and some empty folders which appear to relate to Demo projects which came with Cubase. I attach a screen shot of my content.
Further to this I see the private files VSTSound in Cubase 12 app appear to have been replaced with those from the Cubase 13 app.
I assume reinstalling 12 (or recovering from backup) will correct the private VSTSound files in the Cubase 12 app.
So what I don’t know is why the common file links were there for Cubase 11 and 12 private files which appear to work OK.
I assume why I and some others couldn’t see the Cubase 13 preset was that the common files errors were overriding the apps VSTSound private files as they had the same name and pointed to Cubase 12 private files.
The incorrect registration via the Library fixed the missing presets because it actually replaced the the private files in the Cubase 12 app with those from the Cubase 13 app.
I believe I choose the Steinberg Library registration option of default rather than register in place when it popped up in the Library and now assume this is the difference between those two options.
Not seen any documentation on the Steinberg Library app which actually advises what those options did.
Would appreciate your comments on my observations and how I should fix.
Not sure whether the Library app XML files need rebuilding as well as Cubase 12 private files.
Cheers
David