Identifying race conditions on LightDM startup

Dear all,

recently I installed Manjaro XFCE on an old iMac (
After getting it to boot with the help of the community, I’m stuck at the next problem:
The only thing I see when the GUI starts up is a black screen, the mouse pointer (always), a box with graphical errors (30% of the boots), and/or the top panel with graphical errors (10% of the boots).

Switching to TTY and killing lightdm via systemctl kill lightdm gives me exactly what I want: A graphical user login without any glitches.

So, how do I identify and remove the cause for the possible race condition?

Thank you very much in advance,

Someone might have had a similar issue on arch:

There the solution was to reinstall the lightDM theme.
The topic also cobtains some further links.

I reinstalled lightdm, lightdm-gtk-greeter, lightdm-greeter-settings, and removed all other greeter themes.

I still just see the box with graphical errors etc.
Edit: After upgrading the Kernel from 515 to 61, I am left with just the pointer.

When I kill lightdm in TTY via systemctl kill lightdm, I land on the graphical user login screen, which is exactly what I want.

Could that point to some startup issues where lightdm is being started before some requirements are satisfied? How can I pinpoint that?

Uncommenting logind-check-graphical=true in /etc/lightdm/lightdm.conf gives me just the pointer, followed by a black screen and without the ability to switch to TTY.
Delaying the lightdm startup by up to 30s via ExecStartPre=/usr/bin/sleep 30 in /etc/lightdm/lightdm.conf did not change anything.

I run into similar problems. No possibility to switch to an TTY. Need to start from USB-Stick, remove lightDM and install lxdm/

I done a new install on a NUC computer and If I press ESC on the splash screen, I saw the infinity loop error.

I found, that, if I remove the USB-C cable from PC and use the HDMI for the monitor, lightDM works fine. So, perhaps there is an error with USB-C on startup with a library, used by lightDM?