after acquiring the Absolute Collection 4 in 2019 I ran into pretty much the same problem: some standalone installers (like “The Grand” or “HALion 6”), also many zipped .vstsound container files, etc.
Just as a suggestion:
once you’ve de-zipped whatever you’re about to use, you can put all these .vstsound files anyhwere you like, then just double-click the first one of them (if there are more than one), which would open Library Manager and a pop-up, then choose “register in place”. then after a few seconds you’d find the newly registered extension within their matching section(s) of Library Manager.
For this purpose, I soon decided to make myself a more consistent content file directory, so I put (up to) six category folders inside it, arranged / named exactly like the (up to) six sections within Library Manager - like this:
01_HALion\ …[available content files within their folders]
02_Groove_Agent\ …[available content files within their folders]
03_Cubase-Nuendo\ …[available content files within their folders]
04_The_Grand_3\ …[available content files within their folders]
05_Padshop\ → folder “Zero Gravity” → ADD_SMT_118_Zero_Gravity.vstsound
06_Retrologue\ …[available content files within their folders]
By this simple structure and “Register in place”, any newly acquired content containers wouldn’t even have to be moved away from their default locations in C:\ProgramData\Steinberg\Content\xyz to a self-defined new location, since they’re already at their target locations. Once you’d open Padshop 2 within Cubase, your Zero Gravity extension should be accessible.