Ubuntu 24.04 with lightdm boot up

[IRTonyCHAN]

If device boot up without HDMI/DP cable, lightdm will not autologin, stuck on "Waiting for ready signal"
If device boot up with HDMI/DP cable, everything work fine.
I am not sure which part have an issue, Ubuntu? Xubuntu? lightdm?
I would appreciate it if anyone could help.

[+0.12s] DEBUG: Quitting Plymouth
[+0.13s] DEBUG: Using VT 7
[+0.13s] DEBUG: Seat seat0: Starting local X display on VT 7
[+0.13s] DEBUG: XServer 0: Logging to /var/log/lightdm/x-0.log
[+0.13s] DEBUG: XServer 0: Writing X server authority to /var/run/lightdm/root/:0
[+0.13s] DEBUG: XServer 0: Launching X Server
[+0.13s] DEBUG: Launching process 1186: /usr/bin/X -core :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
[+0.13s] DEBUG: XServer 0: Waiting for ready signal from X server :0
[+0.13s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+0.13s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0