XPS 13 9365 - No boot after brief keyboard lights

I have an XPS 13 9365 with expired warranty that shipped in Sept 2018. It's been a true workhorse for me all these years. However, a few days ago it started suffering from the following behaviors:

• Pressing the power button briefly lights up the keyboard but the computer fails to boot.
• Pressing "D" key plus power button successfully activates screen diagnostics.
• I can consistently duplicate the following diagnostic LED behavior WHEN THE POWER CORD IS PLUGGED IN but I have not found any information online regarding error code or related cause. When the power cord is unplugged, this diagnostic LED behavior is NOT observed. Please note this behavior only involves a WHITE light from the diagnostic LED under the touch pad. NO AMBER light is ever observed.
  1. Long-press the power button for about 20 seconds (the keyboard briefly lights up when the button is first pressed. No light is observed from the center diagnostic LED when the power button is first pressed.
  2. Continue to hold the long-press until the diagnostic LED FLASHES TWICE.
  3. Release the power button.
  4. The diagnostic LED FLASHES FOUR (4) times.
  5. Following the four flashes, the keyboard briefly lights up.

I've attempted the following "solution" that I've found in a number of videos and elsewhere online:

1. Unplug the power cord
2. Remove the bottom cover
3. Remove the main battery
4. Long-press the power button for at least 30 seconds
5. Unplug the CMOS battery
6. Short across the two pins of the CMOS battery socket
7. Reinstall the battery
8. Re-plug the CMOS battery.
9. Replace the bottom cover
10. Plug in the power cord
11. Attempt to boot - to no avail (Press power button. Observe brief keyboard light. Observe no further boot behavior).

I also tried two different variations of the above after removing the battery:

VARIATION 1 (power cord, no main battery, no CMOS battery)

• Plug in the power cord (with no main battery and no CMOS battery)
• Attempt to boot - to no avail.

VARIATION 2 (power cord, no main battery, connected CMOS battery)

• Plug in CMOS battery
• Plug in power cord (with no main battery)
• Attempt to boot - to no avail

Thanks to all for considering my question. Please advise any recommendations.