I have a caddy with an external HD fitted which purports to be Thunderbolt compatible. So I bought a thunderbolt lead to connect it to my iMac, bu on checking System Information no device is shown to be connected to the thunderbolt port. Is it necessary to Initialise a Thunderbolt device or do some suppliers use the term thunderbolt when they should mean USB C?
Can you see the device connected on a USB bus somewhere? That would give you a clue what it was actually doing.
USB-C describes a physical connector and most modern Thunderbolt ports use it. That socket/cable/plug can carry a variety of services including Thunderbolt and Thunderbolt can carry USB format data. I guess that some less scrupulous suppliers might therefore claim Thunderbolt-compatible for devices that you and I would not consider merited that.
I have a USB-3.1 cable and a Thunderbolt 3 cable here, each having USB-C connectors on each end. I was moved to write on each of them what they were because they are so subtly labelled!
Is the socket that it is plugged into on the Mac definitely a Thunderbolt port? The 2021 iMac has two USB-C sockets that are Thunderbolt 3 ports, and two USB-C sockets that only do USB 3.
It is a 2017 iMac with two Thunderbolt ports which are shown on system information but with nothing connected. However the caddy is shown to be connected via USB3.
Just to expand on my previous comment (that reads a little cryptically a day later):
A Thunderbolt port (through its USB-C connector) will automatically configure itself as a USB port if it detects a USB device being connected. That is presumably what you're seeing.
An unscrupulous vendor could say "it connects correctly to a Thunderbolt port so it is Thunderbolt compatible"; that just isn't what the majority of us would expect the words to mean. It would be a bit like Zoom's original claim that it provided end-to-end encryption of video calls: when caught out they effectively said that they had a different definition of what 'end-to-end encryption' actually means than the rest of the industry.
Lionel Ogden 