Manjaro will not boot

[El_Brujo]

It looks like you have already the i915 driver working in kernel mode. So the issue might be similar to the one discussed below:

LightDM doesn't start automatically on boot but works fine if I run it from terminal

Looks like your driver is already working on Kernel mode by default. I would give a try to this: https://wiki.manjaro.org/index.php?title=Configure_Graphics_Cards If that doesn’t help, the problem might be the timing in which the driver is being loaded in the boot sequence. Most likely, lightdm is starting up before the video driver is ready. You might want to play around with Early KMS as explained in the Arch Wiki. Hope the above helps!

EDIT: So, for your case, the issue might be the timing in which GDM boots up.

Hope that helps!