There is also the matter of checking your Spotlight settings and making sure your user folder, or where you save projects, isn’t blocked. But Spotlight is not infallible, it’s a convenience tool for how fast it is, but it doesn’t actually search your disks nor know anything about it. It is searching an index, which can be wrong. The tips above are good for checking that out.
By the way, the best way to run a Spotlight search for Scrivener projects in general is to use the File ▸ Find All Projects in Spotlight. Or, if you have the version sold by Apple, which does not allow software to open Spotlight windows for some reason, then manually type in: kind:Scrivener Project into the search bar. Then ensure that the toolbar has “This Mac” highlighted, and not some folder (which it should by default).
It should be baffling that Apple refused to help you find your files, and provide the kind of basic system troubleshooting you are having to get here, simply because those files were made by another program. But it isn’t baffling, because that is how lazy their tech support is. 
They see the word “Scrivener” and it’s an immediate bounce—we see it almost every day. My advice to anyone contacting Apple support, never bring up the name of any software you use. Speak only in terms of needing to solve a problem abstractly or in relation to the operating system. You lost some files, that is all they need to know. If they ask you what program saved the files, brush it off and tell them that isn’t relevant because you know the file names or whatever.
I digress; people losing track of where they put things, or the operating system losing track of where they went (which is what you see when you right-click in the Dock, the Recent list isn’t technically Scrivener any more), is something that happens. There is a lot of advice here already on the forum worth searching for.
For example, there is this post, for all the times Spotlight doesn’t work. That describes a method of actually searching your files, not the index, and so it will take a long time. For example, in that thread the user accidentally trashed their projects. Spotlight won’t find them if they are trashed, but those steps will.
Feel free to write in to tech support and open a ticket if you want, but there isn’t a lot we can do, other than this, given how you are given the freedom to store things wherever you want, there are no easy answers.