Hello,
I would be happy to help. 
Thank you for all the details and background, that definitely makes it a bit easier to get a sense of what’s going on. Also I’m sorry you’re going through all this; I can only imagine it sounds like a headache and a half and that sounds like a very rough position to be in. 
From there, my honest take is that, for something like this where you’ve been syncing to OneDrive and involving the installation of a collection on a new machine, you’re likely into a bit of depth that goes a bit beyond AnkiHub and are pretty firmly in Anki software issues now, I’m sorry to say. Which may necessarily extend beyond our expertise
Given the extent of what you’re looking at, my honest take is that you would likely be better set up by checking out the official Anki forums where there is a bit more expert help with technical Anki details and the like. A number of die-hards and developers hang out over there, and if there are answers to be found that will be the place to find them. Similarly, they can look at your AnkiWeb collection and backups in a way that we’re not able to (https://forums.ankiweb.net/)
From everything I can gather, it sounds like potentially a media or server glitch on the AnkiWeb side, which unfortunately we’re not well poised to be able to help with here as it’s a separate service and I don’t have direct access or insight into those things, sadly
It may be that they’ll have access to server copies of your collection and, even if not, they will undoubtedly be the best source of help with the issues you’re having. Since your AnkiHub account has been inactive for some time, and you haven’t been syncing with the AnkiHub servers recently, it’s a bit outside of what I’m likely to be able to help with, I’m sorry to say, as we don’t store any of your local collection or media, and any goings-on with the AnkiWeb servers would likely be best handled by the Anki forums folk
A few things I’ll point out in the meantime, though, just to give you a sense of what stands out to my eyes (and what may be helpful to focus on if and when you chat with the Anki folks):
It seems a little unusual to me that you wouldn’t have any backups between presumably late 2025 and April of 2026; usually Anki makes multiple backups a day and you should have at least a handful from this year. I can’t say much as to what may have happened there, but it strikes me as being unusual
From there, you should be able to restore from a backup file by double-clicking the file (I believe), or restoring from backup from within Anki: File - Restore from Backup, then select the backup file from which you want to restore. From what you shared, it appears that the file may be zipped, and it may be that the file needs to be unzipped before Anki can make use of it (backups are normally stored as .colpkg files, FWIW.
Sadly, that may be a OneDrive question. I can’t say if that’s even within the purview of AnkiWeb to be able to ascertain, potentially. But they would likely be better-suited to being able to answer this for you, ultimately
It’s possible, yes.
You might double-check with the AnkiWeb folks, but I don’t believe that backups hold or restore media files. Unless they were somehow deleted, those media files should hopefully still be stored locally somewhere, though. Likely they would know best
In theory, it shouldn’t have. But, it may be that it compounded another issue that was present (with OneDrive or similar) in having synced your media. I’m afraid I can’t say for certain
At the very least, if I were in a similar situation the first thing I would do is head over to the Anki forums. They are the most expert help you can find for Anki-related issues and troubleshooting, and if there is advice to be found that will be the place to find it
Best of luck, and please keep us informed as to what you find just in the event that we’re in a position to be of help with others in potentially similar conditions in the future.