Black screen with mouse cursor when connecting to external monitor with lid closed

I am trying to use my laptop in a docked mode, so external monitor, mouse and keyboard with the lid closed. I found this post but didn't much and was very old and have tried to the following.

In gnome tweak tool I've unticked 'suspend when lid is closed'.

and downloaded caffeine gnome extension to try and prevent sleeping etc.

However, I simply get a blank screen with the mouse cursor still working, the laptop does not suspend though.

Any ideas?

Edit: also set HandleLidSwitchDocked=ignore in my login.conf.