T470 to iMAC so that iMAC is ´monitor

[koden]

Hi

My old T420 work laptop I used to connect to my imac with displayport cable.
As soon I connect it my imac switched to show my laptop.

Now I got new T470 laptop.
It has no displayport or minidisplayport.

But it has a HDMI port.

I then bought a HDMI to mini displayport (minidisplayport in imac).

But is not working.

Then I took my T470 docking with me home. It has also the displayport.
With my old displayport cable from T420 I then tried to connect to imac.
No luck.

Could there be some function on my T470 I have to enable to get either docking displayport og Laptop HDMI to work?