shutdown – Manjaro no longer shuts down

Since a few days ago, shutting down Manjaro just leads to a black screen with the mouse cursor.

There is usually another bootable drive connected to the system, but this wasn’t a problem before. Consequently, I believe this is the result of a recent system update, but I can’t be sure.

Following advice from a forum thread, I tried editing /etc/default/grub. Locating the following line:

    GRUB_CMDLINE_LINUX_DEFAULT="quiet udev.log_priority=3"

I first added acpi=force, then, seeing no change, apm=power_off:

    GRUB_CMDLINE_LINUX_DEFAULT="quiet udev.log_priority=3 acpi=force apm=power_off"

I did run a sudo update-grub command after each attempt, before shutting down.

I’ve read that ACPI arguments do nothing if the system has no /proc/acpi/ directory, which I do have. I haven’t been able to determine whether the system has or uses APM.

What is preventing Manjaro from shutting down properly?