LG monitor keeps disconnecting from M2 MacBookPro

Hello,

I had no problem using my 2023 MacBookPro M2 Max with my external LG monitor via a single Thunderbolt cable until last night.

Now it keeps disconnecting and reconnecting when my laptop is open.

Preferences > Displays clearly shows the number of displays fluctuating between one and two.

I have to close the clamshell to make it stop, which has serious drawbacks:

• I lose a screen.
• I can't use the laptop microphone.
• I don't want to use an HDMI connection because it's inferior, and I would need another cable to power the laptop.

I know it's a software problem because I managed to have both the laptop display, and the LG display on at the same time, by adding an iPad to the mix (Sidecar wired connection in mirroring mode).

The LG display was happily running my usual resolution then: 3360x1418 HiDPI

Config:

• Laptop: 16" 2023 MacBookPro M2 Max, macOS Ventura 13.3.1 (22E261)
• Monitor: LG 34"UltraWide 5K 34WK95U-W
• Connection: Thunderbolt

Things I have tried:

• Reboot
• Safe Mode
• Change resolution of the builtin display.
• Change the resolution of the external display via three means: Preferences > Displays, CLI (Display Manager) and GUI (SwitchResX). I can't do it while the laptop is open because the external display does not stay connected long enough. If I do it while the clamshell is closed, the problem comes back after I open the clamshell.
• Delete windowserver plists in ~Library/Preferences/ByHost directory.

I basically need a way to force macOS to forget this monitor. macOS clearly remembers it, and applies different settings for each config (clamshell closed, two-display: clamshell open, three-display: clamshell open + iPad sidecar).