Solved 24H2 external screen not detected anymore

ASUS SCAR 18 (2023) BIOS 331 with 4090 laptop and external monitor connected with Thunderbolt (DP1.4). External screen is simply not detected (no signal) anymore after 24H2 update. Was working fine with 23H2.
It seems a common issue: How to fix 2nd display not working after 24H2 update (Microsoft Answers)

How can MS expect to release such a disastrous edition clearly in alpha/beta to the public?

So I found in Device Manager the yellow triangle for: UCM-UCSI ACPI (Error 43 ) + Intel(R) PC Express Root Port #25 - 7A48 + Intel(R) PC Express Root Port #9 - 7A30. Didn't go away with Shutdown or disable/re-enable/uninstall from Device Manager.

1. I unplugged AC and shutdown Windows 11
2. kept pressed power button for 40secs (keyboard leds lighten up but I ignored this and kept the button)
3. laptop totally turned off at this point. Waited 60 secs more, then pressed the power button once to wake it up as usual and the PC booted as expected. Problem solved, BIOS reset, no more yellow triangles, external monitor working again, and AC plugged back in!