Looking for help debugging a/xrandr

Two days ago I reinstalled EOS with i3.
Most things were pretty easy to set up, but I’m now running into an annoying problem with arandr (probably an xrandr issue under the hood) that I’m not sure how to debug properly.

The issue is that when I connect my external monitor and enable it in arandr, the internal screen goes black and I only see the mouse cursor (which still moves) and nothing happens on the external display.
The only way out of this state seems to be a hard reboot.
I’ve tried setting up autorandr to make it switch back to only the internal display when the external is disconnected, but this didn’t work. I also cannot access the other TTYs (ie ctrl+alt+F1-7).

I would appreciate any tips on how to debug this as I have no clue (journalctl tell me nothing about xrandr, so I don’t even know where to start).

Are there both active in arandr screen?
Ctrl+Return (Apply)
Layout / Save As ~/.sceenlayout/monitor.sh
chmod +x ~/.sceenlayout/monitor.sh

grep monitor .config/i3/config

# uncomment the next line, use arandr to setup displays and save the file as monitor:
exec --no-startup-id ~/.screenlayout/monitor.sh

If you connect the 2nd monitor run
possibly with a shortcut. Or did not I understand this black screen thing, did I?
OR make 2-3 xrandr scripts see monitor.sh and choose one of them with keyboard shortcuts.

No, the internal is active and external is not. The issue happens when I tick the ‘active’ box for the external display and then click apply.

I will try mapping the only internal config to the a shortcut and see if that runs when the screen turns black.