Let me understand the Thunderbolt/USB 4 ports of the new iMac The top model of the new iMac to be launched by the end of May 2021, is said to come with 2 Thunderbolt/USB 4 ports and 2 USB 3 ports.
In my mind, Thunderbolt is a physically different connector compared to the other 2 USB 3 ports, but looking at this picture they are apparently the same port.
I have an old 2012 iMac connected to two external TVs through the thunderbolt port. Each port using a thunderbolt to HDMI dongle. I am not mirroring the main screen. I have 3 independent monitors, the iMac one and each TV.
So I thought, I could do the same to this new iMac. I disconnect the dongles I have on the old iMac and connect to this new one but apparently these &quot;thunderbolt&quot; ports of the new iMac are in fact USB-C ports that deliver thunderbolt. So, In fact I need USB-C to HDMI dongles, right?
So, physically speaking, this new iMac only has 4 USB-C ports, two of them being able to deliver &quot;thunderbolt&quot;, right?
This new iMac has two of these &quot;thunderbolt&quot; ports but apparently if I use both, I will not get two external independent monitors right?
Why?
There's actual more than one version of Thunderbolt - this seem to be the thing that confuses you regarding the connectors.
Thunderbolt (1st generation) which you have on your old iMac uses the same connector as mini-DisplayPort.
Thunderbolt 3, which is on the new iMac, uses the USB-C connector.
Then there's the matter of signalling protocols. The same signalling protocol can potentially be used on several different connectors. This seems to be the source of your confusion on the USB connectors.
Thunderbolt 3, USB 4 and USB 3 signals can run through the same type of connector - namely the USB-C connector.
However, it is also possible to run USB 3 over other connectors, such as the most common USB-A connector that you know from your old iMac.
You're right in that you cannot reuse your old display cables. These were actually not Thunderbolt to HDMI dongles, but rather mini-DisplayPort to HDMI. The new iMac uses a different connector, so they cannot be reused.
For the new iMac you need a USB-C to HDMI cable. You can also use an adapter/dongle and reuse an existing HDMI-to-HDMI cable for the long run of the cable.
The reason you do not get to connect two external, independent monitors is simply that the graphics processing unit in the iMac does not support more than 2 displays - the internal display and a single external monitor. It is not a limitation with the Thunderbolt/USB-C connector, nor is it a limitation with Thunderbolt signalling or anything like that. It is simply the GPU that does not support more displays.