Just to be clear, nothing is “lost”, and there is no need to recreate anything at all. There are ample methods for viewing your data if need be. What we are seeing here is merely a matter of the built-in viewer having been broken in an OS update. It requires a patch to make it functional again since Apple is never going to fix it; can’t say when that will be available yet, though.
- On a one-by-one basis: hit ⌃⌘O (or click the little open-in-external-editor button in the footer bar). WebArchive opens in a window using Safari. Net result: much like using Quick Reference—or viewing any type of material you put into Scrivener that it itself cannot view in the main editor. It’s the same thing you’ll be doing for an Excel spreadsheet, or even a PDF or image if you wish to do more with it than just look at it.
- Bulk use: select all needed files in the binder and press ⇧⌘E (or use File ▸ Export ▸ Files…). You will be asked to name a folder on the disk, into which the .webarchive files will be placed. These files can now be more easily managed with Finder, or with other utilities that support them.
- [Destructive] Convert to industry standard text: select the .webarchive(s) in the binder and use the Documents ▸ Convert ▸ Web Page to Text menu command. As noted, this is a one-way process. If you wish to keep the originals, then duplicate a set of copies and run the command on the duplicates.
⠂─────── ⟢⟡⟣ ─────── ⠂
Going forward, and to digress a little, I’d give considerable thought to archiving material as text instead of in a proprietary single-operating system format like WebArchive. PDF is also a good alternative, especially if for some reason the presentation of the content is of importance—some sites even have a function for doing that right in the page (like Wikipedia). With Scrivener you can enable text archival in the Sharing: Import preference pane, with the Convert imported WebArchives and web pages to text setting.
At the very least, you will be saving yourself from actual loss and having to recreate everything, should Apple ever discontinue support in the next 40 years, or if for whatever reason you find yourself having to migrate to another operating system.
I’ve never used this format myself, the above being the strongest reasons for why. I also have concerns about how good it is for actual archival since it leaks to the Internet like a sieve when you view them. That also raises privacy concerns. If so much as having your Preview column open in Finder means tracking and advertising data is being sent from your computer to all of these sites, unimpeded by any of the browser extensions you may typically employ to protect yourself, that’s a problem. And since it is, in some regards, an “archive”, it is saved under whatever protections the law afforded you at that time, but not under whatever laws protect you now. A page from 2007 is not going to adhere to the GDPR. There are also security concerns when you have ancient site code being executed like that.
Sorry for the semi-off-topic rant, but in my book any time there is a glitch with WebArchive is a good time to point out its numerous flaws, as one has time to consider whether or not its a good format to continue using, when it stops working.