[Bug 1938999] Re: External displays not working on Thinkpad T490 with ThinkPad Thunderbolt 3 Dock

I also installed the 5.13.9 kernel, again with the same unmet
dependency:

dpkg: dependency problems prevent configuration of linux-headers-5.13.9-051309-generic:
linux-headers-5.13.9-051309-generic depends on libc6 (>= 2.33); however:
Version of libc6:amd64 on system is 2.31-0ubuntu9.2.

To my surprise, I was able to boot using this kernel.
Package manager complains due to broken packages.
Also, I am unable to gather some of the logs:
cat: /proc/version_signature: No such file or directory
dmesg: read kernel buffer failed: Operation not permitted

Nevertheless, the displays work as they should. I'm attaching the logs I
got.

** Attachment added: "Logs from 5.13.9 with nvidia-driver-470"
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1938999/+attachment/5517306/+files/logs_2021-08-11_5.13.9-051309-generic_nv470.zip

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https://bugs.launchpad.net/bugs/1938999

Title:
External displays not working on Thinkpad T490 with ThinkPad
Thunderbolt 3 Dock

Status in linux package in Ubuntu:
Confirmed

Bug description:
I have two external displays chained via Display port connected to the
ThinkPad Thunderbolt 3 Dock.

They are working with kernel 5.8.0-63 but not with the new 5.11.0-25
kernel.

I could reproduce this behavior several times for both kernels, as
follows: I booted up with disconnected dock, logged in, then I
connected it, disconnected it, and connected it again.

With the 5.11.0-25 kernel the external displays go black; the main
screen turns off and on several times. Sometimes the main screen
remains working, but UI is lagging.

I'm attaching the logs. Two separate boots for each variant are marked
'a'/'b'.

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