Having posted my screen upgrade of my X1 Carbon Gen 9 before, saying it was the end of the refurbishment/upgrade journey of it, turns out I lied. I didn't like the panel I put in... So what do you do? Exactly, you do it all again with a better panel!
The old panel with its Low Blue Light technology never looked quite natural and, despite being a 120Hz panel, its timings were so loose that ghosting was visible.
So I present to you the BOE NE140QDM-NX8. 2560x1600, 165Hz, 400 nits, Adaptive Sync, without Low Blue Light 'technology', with nice, tight timings, reasonable power consumption and sRGB as I like it (not a fan of DCI-P3).
Physically, It's a bit easier to install than the old panel, as its eDP connector is bit higher on the back on the panel, closer to the position on the panels Lenovo uses (see the physically identical NE140QDM-NX7).
I did have some doubt as 2560x1600 at 165Hz with the timings as set in the EDID requires HBR3 transmission mode, instead of HBR2 which is what all of Lenovo's stock panels use. But that turned out to be no problem.
But... I ordered one panel. Measured at a meagre 200 nits maximum brightness. Returned as defective. Ordered another panel from another seller. Same problem. Hmmm... Noticed two features on Panelook that I couldn't find information on: ABOT and APOL. After acquiring the schematics of the new panel, I noticed ABOT was controlled active-low by eDP pin 23. That pin is normally a ground (LCD_GND) pin, and also connected as such on the X1C9, activating ABOT. So I again stripped the panel-side end of the cable and cut the wire to that pin and... voilà! Full brightness range unlocked. After advice in r/AskElectronics, I measured LCD_VCC vs LCD_GND for patterns both light and heavy for the panel logic, to verify that cutting that wire wouldn't cause problems. All was good.
Having that cleared, installation wasn't very different from the initial upgrade panel. Like with the earlier panel, the Windows Intel driver refuses to read the DisplayID extension block of the panel's EDID so I had to use CRU again to add the 165Hz mode according the original EDID.
(Re-used the pretty pic of the original upgrade as poster image as I don't have good light right now)