Target Display mode question

Hi all,

I am trying to use an old 2010 27" iMac as a display for a 2018 13" MBP as described here :https://support.apple.com/en-us/HT204592

I believe they both fit for this usage ?

I use a thunderbolt cable along with an usb-c adapter for the mbp (both apple originals) and followed the procedure described here : https://support.apple.com/en-us/HT204592.

Yet it doesn't work.

Is there something else I should do or be aware of ?

Is there another way to test the thunderbolt to usb-c adapter ? I suspect he might be fautly.

Any other ideas ?

Thanks,

Thierry