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Eh?

Yes they can tell if you use TOR. TOR is like a VPN, it can be detected but it doesn't tell the ISP what you are doing while you use it.

They don't know what's going on if you are a user or an intermediate node.

If you are an exit node they see all the traffic in clear.

Sorry, I thought the context was clear. I was talking about an end user as described in the OP.

Yes, if its an exit node that is the case.