Does a "Non-Destructive" JPG exists?

Almost no file format will allow perfect reversion to pre-editing state. For example, what if you cropped half of the image out? You'd need a file that had both the original and the final saved version. You CAN do that with a DNG file that contains non-destructive edits from ACR/Lightroom, but otherwise no.

There can be non-destructive editing of a JPG file, which is how Adobe Camera Raw, Lightroom, and how many newer consumer and mobile apps do it such as Apple Photos.

Although the JPG file itself will undergo degradation if edited and then saved back to the same file, that can be avoided if the edits are stored separately from the image file as metadata, such as in a database. By storing the edits separately, it’s possible to “revert” the JPG to its original state. But that’s not what really happened, the reality is that the edits were never actually applied to the original JPG.

This is how it works on an iPhone, for example. If someone sends me a JPG and I edit it on my iPhone, it’s always possible to snap it back to its original state because it silently created a copy that is shown to me as the edited version. I just have to tap the Revert button, and it swaps the original back in to show me.

Because this question was posted in the Photoshop community, the first thing to say is that this is not something you can do with Photoshop. If you edit a JPG in Photoshop and save that, the original pixels are directly edited and so saving that slightly degrades the image after JPEG compression is re-applied. An alternative is to open the JPG, edit it (maybe after saving that as PSD or TIFF as you mentioned), save/export a JPG copy, and don’t save changes to the original JPG. But then you would be aware that you are now managing multiple files. The way you get back to the original is to use it instead of the copy.

If Adobe Camera Raw or Lightroom were used, those work like Apple Photos: They store and render the edits separately from the original image file, so to see the original again you just revert (throw out) the edit metadata.

Maybe it was a DNG file-type.

A DNG file ( If converted from a raw camera file) can contain the raw data and editing metadata that is recognised in Adobe Photo apps, and can be re-edited (back to original state).

No such thing.

Jpeg compression is always destructive and non-reversible. No exception.

There are "de-jpeg" algorithms to remove/restore the artifacts, with varying success. Photoshop has an ai based de-jpeg neural filter, which is reasonably effective. But of course, it's still guessing, just making better guesses.