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Seems like it's clearly a client, but Meta calls it a "clone site":

Looks to me like a patched client a la vanced: https://www.theogapp.com/

It is a clone of the client, so both.

Instagram is a platform. It’s not a clone of that just like Tweetbot is not a clone of Twitter.

Yes, a client is not necessarily a clone. But this one is, that's the point