The issue is not fully over yet 
I had to check and suspended computer. My AC wasn't plugged off but after waking up, there was no wifi and I had again wlan0 as DOWN and DORMANT. However, this time all elements were in place so system wasn't so unresponsive and vague to commands as before.
Right after suspend I got:
● NetworkManager.service - Network Manager
Loaded: loaded (/usr/lib/systemd/system/NetworkManager.service; enabled; vendor preset: disabled)
Drop-In: /usr/lib/systemd/system/NetworkManager.service.d
└─NetworkManager-ovs.conf
Active: active (running) since Thu 2020-03-26 16:58:55 CET; 40s ago
Docs: man:NetworkManager(8)
Main PID: 982 (NetworkManager)
Tasks: 3 (limit: 9370)
Memory: 14.7M
CGroup: /system.slice/NetworkManager.service
└─982 /usr/bin/NetworkManager --no-daemon
mar 26 16:58:56 alienware-PC NetworkManager[982]: <info> [1585238336.3329] device (wlan0): new IWD device state is disconnecting
mar 26 16:58:56 alienware-PC NetworkManager[982]: <info> [1585238336.3330] modem-manager: ModemManager available
mar 26 16:58:56 alienware-PC NetworkManager[982]: <info> [1585238336.3333] device (wlan0): new IWD device state is disconnected
mar 26 16:58:56 alienware-PC NetworkManager[982]: <info> [1585238336.3336] manager: startup complete
mar 26 16:59:00 alienware-PC NetworkManager[982]: <info> [1585238340.3383] agent-manager: agent[40e6bec3c3d0f8ce,:1.24/org.kde.plasma.networkmanagement/1000]: agent registered
mar 26 16:59:00 alienware-PC NetworkManager[982]: <info> [1585238340.9737] manager: NetworkManager state is now ASLEEP
mar 26 16:59:03 alienware-PC NetworkManager[982]: <info> [1585238343.5634] manager: (A0:B4:A5:12:B5:46): new Bluetooth device (/org/freedesktop/NetworkManager/Devices/4)
mar 26 16:59:14 alienware-PC NetworkManager[982]: <info> [1585238354.8616] audit: op="radio-control" arg="wireless-enabled" pid=1273 uid=1000 result="success"
mar 26 16:59:17 alienware-PC NetworkManager[982]: <info> [1585238357.4873] audit: op="radio-control" arg="wireless-enabled" pid=1273 uid=1000 result="success"
mar 26 16:59:18 alienware-PC NetworkManager[982]: <info> [1585238358.5330] audit: op="radio-control" arg="wireless-enabled" pid=1273 uid=1000 result="success"
Now I see that NetworkManager state is now ASLEEP
and also, new IWD device state is disconnected
After
sudo ip link set wlan0 mode default
sudo systemctl restart NetworkManager
wifi was still no go and info changed a bit:
● NetworkManager.service - Network Manager
Loaded: loaded (/usr/lib/systemd/system/NetworkManager.service; enabled; vendor preset: disabled)
Drop-In: /usr/lib/systemd/system/NetworkManager.service.d
└─NetworkManager-ovs.conf
Active: active (running) since Thu 2020-03-26 17:07:44 CET; 12s ago
Docs: man:NetworkManager(8)
Main PID: 2173 (NetworkManager)
Tasks: 4 (limit: 9370)
Memory: 4.7M
CGroup: /system.slice/NetworkManager.service
└─2173 /usr/bin/NetworkManager --no-daemon
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4364] device (lo): carrier: link connected
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4366] manager: (lo): new Generic device (/org/freedesktop/NetworkManager/Devices/1)
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4374] manager: (eth0): new Ethernet device (/org/freedesktop/NetworkManager/Devices/2)
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4385] manager: (wlan0): new 802.11 Wi-Fi device (/org/freedesktop/NetworkManager/Devices/3)
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4536] device (wlan0): new IWD device state is disconnected
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4545] modem-manager: ModemManager available
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4559] agent-manager: agent[e4630cd24d95b5da,:1.26/org.kde.plasma.networkmanagement/1000]: agent registered
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4567] ovsdb: Nie można połączyć: Nie ma takiego pliku ani katalogu
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4618] manager: (A0:B4:A5:12:B5:46): new Bluetooth device (/org/freedesktop/NetworkManager/Devices/4)
mar 26 17:07:44 alienware-PC NetworkManager[2173]: <info> [1585238864.4636] manager: startup complete
As usual, reboot did nothing and wlan0 was going back to be DORMANT.
There is still some issue with ovsdb, whatever it is. Do you know what ovsdb is or where does it come from?
In the end, I launched the restart service and that full load of scripts did the trick and the wifi is working. I'm not sure if after reboot my wifi will be still working.
The irritating part is that I have both countermeasures for wifi not being stopped during suspend and yet it is switched permanently off and won't wake up by itself.
The issue remains but the main thing is, I have a quick way to start wifi:
set wlan0 to DEFAULT
use networkmanager restart service
This installation is over 3,5 years old and till now I didn't have any issues with wifi. But to be honest, a few months ago situation got worse and I had the need to add this restart service and now it became even worse.
Maybe we finally get to the bottom of this? Something is still missing.