This is NOT related to these bugs:
https://bugs.kde.org/show_bug.cgi?id=426985
https://gitlab.freedesktop.org/upower/upower/-/issues/126

Similar but not the same, so please do not tell me its been resolved in 6.6 by Nate Graham. Not the same. Similar, but not.

Short Version:
Random cutting off the power and fully discharging the batteries without warning. Pressing the power button does nothing as the external power supply is cut off and all batteries drained (unless you cach it in the middle of draining).

I already thought I have narrowed it down, but still I am confused. So these are the steps I have already done:

0. Laptop has always been updated. All firmawares and UEFI have been updated (LVS and uefi via .iso). So no issues with broken firmware/uefi. All internal test of lenovo have been conducted (4 hrs). Before installing the system nvme cells have been cleaned (hdparm/sleep does not work, done via specialized lenovo software). All good, tip-top.

Before reporting here, I have done the following:
1. I bought new, geniune power supply (new revision via lenovo service codes).
2. I changed 3 pin cord to power supply (good one) and removed extension cord (good one); just in case.
3. I'm using rolling release and it seems to be a regression.
4. I cannot see ANYTHING via $ "upower -d". Absolutely nothing, either in 1.90 or 1.91
5. I checked another distro to be sure (Debian) to see what "upower -d" shows. Same as in Arch. All good. 
5. I tried all combinations imaginable for 4 days/nights. I thought I have narrowed it down, but now cannot replicate it.

The colsest of reproducing the bug was using Arch and doing the following:

Version 1:
1. Middle click battery in tray
2. Go to menu and search "lock". Lock the screen.
3. Go to bed.
4. Check the next morning.

Version 2:
1. Work as you normally do. Go for a break/leave
2. Make the laptop go to sleep and let it lock and turn off the screen.
3. Come back after some time.
4. Now battery is discharging, power supply cord is cut off (small diode next to usb-c is off, of course).

I've done all combinations and I'm buffled of the randomness.
The CLOSEST of the idea what makes the power supply being cut-off is LOCK SCREEN. But it seems random now.
I'm stunned. Constant discharging battery (even fully) and doing so many cycles will kill the battery for sure.

So here is the result of $ upower -d (useless as it seems everything is OK):

---
Device: /org/freedesktop/UPower/devices/battery_BAT0
  native-path:          BAT0
  power supply:         yes
  has history:          yes
  has statistics:       yes
  battery
    present:             yes
    rechargeable:        yes
    state:               fully-charged
    warning-level:       none
    technology:          lithium-ion
    charge-start-threshold:        75%
    charge-end-threshold:          80%
    charge-threshold-supported:    yes
    icon-name:          'battery-full-charged-symbolic'


Device: /org/freedesktop/UPower/devices/battery_BAT1
  native-path:          BAT1
  battery
   power supply:         yes
    present:             yes
    rechargeable:        yes
    state:               fully-charged
    technology:          lithium-polymer
    charge-start-threshold:        75%
    charge-end-threshold:          80%
    charge-threshold-supported:    yes
    icon-name:          'battery-full-charged-symbolic'
 
Device: /org/freedesktop/UPower/devices/line_power_AC
  native-path:          AC
  power supply:         yes
  has history:          no
  has statistics:       no
  line-power
    warning-level:       none
    online:              yes
    icon-name:          'ac-adapter-symbolic'

Device: /org/freedesktop/UPower/devices/line_power_ucsi_source_psy_USBC000o001
  native-path:          ucsi-source-psy-USBC000:001
  power supply:         yes
  has history:          no
  has statistics:       no
  line-power
    warning-level:       none
    online:              yes
    icon-name:          'ac-adapter-symbolic'

Device: /org/freedesktop/UPower/devices/line_power_ucsi_source_psy_USBC000o002
  native-path:          ucsi-source-psy-USBC000:002
  power supply:         yes
  has history:          no
  has statistics:       no
  line-power
    warning-level:       none
    online:              no
    icon-name:          'ac-adapter-symbolic'

Device: /org/freedesktop/UPower/devices/DisplayDevice
  power supply:         yes
  has history:          no
  has statistics:       no
  battery
    present:             yes
    state:               fully-charged
    warning-level:       none
    charge-cycles:       N/A
    percentage:          94.5197%
    icon-name:          'battery-full-charged-symbolic'

Daemon:
  daemon-version:  1.91.0
  on-battery:      no
  lid-is-closed:   no
  lid-is-present:  yes
  critical-action: HybridSleep

On Debian upower shows the same. No clue what cased the regression suddenly :(.