По поводу тиринга, не все так однозначно: многие успешно справляются с этой проблемой, даже я это делал, причем на этом компьютере только с другой операционкой. На стационаре тоже вылечил, который на той же Kubuntu 18.04, но тут имеется различие в версионности драйверов и самой аппаратной части.
И однако этот опыт вновь не подвёл: теперь наблюдаю знаменитую иллюстрацию «тайна темного экрана». Проблема однозначно в чём-то другом, с выводом на экран система справлялась прекрасно
sudo cat /var/log/messages | grep failed
May 1 19:35:04 LINUX kernel: [ 0.138489] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 19:35:09 LINUX sddm-greeter[680]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 19:50:49 LINUX sddm-greeter[2234]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 20:20:25 LINUX sddm-greeter[12718]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 20:22:37 LINUX kernel: [ 0.138491] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 20:22:42 LINUX sddm-greeter[648]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 20:31:55 LINUX kernel: [ 0.138470] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 20:32:02 LINUX sddm-greeter[700]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 20:36:40 LINUX kernel: [ 0.138483] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 20:36:46 LINUX sddm-greeter[681]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 20:38:10 LINUX kernel: [ 0.138411] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 20:38:16 LINUX sddm-greeter[666]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 20:42:54 LINUX kernel: [ 0.134481] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 20:43:00 LINUX sddm-greeter[704]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 20:47:03 LINUX kernel: [ 0.134435] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 20:47:09 LINUX sddm-greeter[677]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 20:48:00 LINUX sddm-greeter[1251]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 21:09:18 LINUX kernel: [ 0.138659] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 21:09:26 LINUX sddm-greeter[683]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 21:25:43 LINUX kernel: [ 0.138522] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 21:25:50 LINUX sddm-greeter[694]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 21:43:12 LINUX kernel: [ 0.138544] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 21:43:17 LINUX sddm-greeter[671]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 22:07:33 LINUX kernel: [ 0.138447] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 22:07:41 LINUX sddm-greeter[704]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 22:13:42 LINUX kernel: [ 0.138548] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 22:13:48 LINUX sddm-greeter[702]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 22:19:23 LINUX sddm-greeter[1290]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 22:31:43 LINUX kernel: [ 0.138527] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 22:31:49 LINUX sddm-greeter[686]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 22:44:33 LINUX kernel: [ 0.134443] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 22:44:40 LINUX sddm-greeter[703]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 22:48:22 LINUX kernel: [ 0.138460] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 22:48:30 LINUX sddm-greeter[679]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 22:53:53 LINUX kernel: [ 0.138439] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 22:54:00 LINUX sddm-greeter[666]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 23:00:57 LINUX kernel: [ 0.134472] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 23:01:03 LINUX sddm-greeter[660]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 23:04:35 LINUX kernel: [ 0.138473] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 23:07:29 LINUX kernel: [ 0.138460] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 23:11:10 LINUX kernel: [ 0.138547] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 23:11:15 LINUX sddm-greeter[695]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 23:13:22 LINUX kernel: [ 0.138475] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 23:13:30 LINUX sddm-greeter[715]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 1 23:14:30 LINUX kernel: [ 0.138437] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 1 23:14:36 LINUX sddm-greeter[693]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 2 10:26:05 LINUX kernel: [ 0.134424] acpi PNP0A08:00: _OSC failed (AE_ERROR); disabling ASPM
May 2 10:26:13 LINUX sddm-greeter[733]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
May 2 10:32:50 LINUX sddm-greeter[2173]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
Да, драйвера свободные, как при начальной установке и в рабочем состоянии, поскольку с выводом изображения как раз-таки все в порядке. А вот с самим KDE..
spoiler
VGA compatible controller: NVIDIA Corporation GK106 [GeForce GTX 650 Ti] (rev a1) (prog-if 00 [VGA controller])
Subsystem: Palit Microsystems Inc. GK106 [GeForce GTX 650 Ti]
Flags: bus master, fast devsel, latency 0, IRQ 31
Memory at f6000000 (32-bit, non-prefetchable) [size=16M]
Memory at e0000000 (64-bit, prefetchable) [size=128M]
Memory at e8000000 (64-bit, prefetchable) [size=32M]
I/O ports at e000 [size=128]
Expansion ROM at 000c0000 [disabled] [size=128K]
Capabilities: [60] Power Management version 3
Capabilities: [68] MSI: Enable+ Count=1/1 Maskable- 64bit+
Capabilities: [78] Express Endpoint, MSI 00
Capabilities: [b4] Vendor Specific Information: Len=14 <?>
Capabilities: [100] Virtual Channel
Capabilities: [128] Power Budgeting <?>
Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 <?>
Capabilities: [900] #19
Kernel driver in use: nouveau
Kernel modules: nouveau
P.S.: горьким экспериментальным опытом научен, что проприетарные драйвера не так уж стабильны и хороши.
Бесполезно.. Ошибка как была так и остаётся, а вот время бесследно улетучивается, поэтому решил перейти на docker. В текущих условиях это единственно возможный и верный путь. Если найду первоисточник проблемы и смогу его устранить - обязательно отпишу сюда. Быть может, кому-то да поможет