The effect that the output comes down to a crawl when the lid is closed is a know bug that hasn’t been fixed so far.
https://forums.developer.nvidia.com/t/525-60-11-breaks-composited-desktop-on-x11-if-laptop-lid-is-closed/236181?u=generix
It shouldn’t crash on mirror, nevertheless. In your Xorg logs, the modesetting driver has an issue:
[ 12.813] (EE) modeset: Failed to load module "glamoregl" (module does not exist, 0)
[ 12.813] (EE) modeset(0): Failed to load glamor module.
The module should be provided by the xorg-server package and reside in /usr/lib/xorg/modules/libglamoregl.so
https://archlinux.org/packages/extra/x86_64/xorg-server/
I think the path is missing from what you set in xorg.conf, rather delete it.