I have a (relatively old, from 2012) Samsung monitor that works fine with a VGA connector with OSx. The model is either S27A550H or S27B550V. I don’t think they have firmware I can update unlike newer monitors (?), but I might have missed my search.

However, it doesn’t work with HDMI. The monitor seems to have two HDMI sockets, one is HDMI1 and one is HDMI2/MHL.

I connected an HDMI cable between the Macbook Pro and the monitor, in both connectors, but the monitor reports “No signal”.

The strange thing is that the monitor never scans HDMI1 regardless of where I plug in the HDMI cable. It goes only over HDMI2/MHL. But I am not sure if that’s the issue. I should mention that the HDMI cable is connected to the Macbook Pro through USB-C with an adaptor (freshly bought from Amazon).

When I take in/out this cable from the Macbook, the laptop display does “blink” and I think the screen is also making an attempt to connect (?) – but it just doesn’t work.

I looked around to try and troubleshoot this, but nothing I could find that would solve the problem.