Illustrator does not do backups. That is not how that feature works.
It is supposed to save a special file every x minutes that can then be recovered when Illustrator crashes. BUT: if it happens to save that file while Illustrator is crashing, then the file is toast. And btw any file will probably be toast if it gets saved while a crash is happening. That's the reason why you should also never rely on only one copy of a file, but have backups.
If you want to have backups, get the plugin Autosaviour. There's even a free version available, which will give you one backup copy of your file. And then of course: save regularly. Save on different volumes. Save different versions. Keep Time Machine running. Just the basic stuff.
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