Comment 105 for bug 1874194

Lenovo Legion 5 15IMH05

$ uname -rv
5.11.0-34-generic #36~20.04.1-Ubuntu SMP Fri Aug 27 08:06:32 UTC 2021

NVIDIA Driver Version: 470.63.01

Had the same issue for some time, until I've "fixed it" recently. The problem appeared out of nowhere after some update. Booting with attached external monitor no matter if attached to HDMI or to DP over USB-C resulted in total freeze during Ubuntu splash screen (for me worse then BSoD from the rival product, couse no feedback what's going on...).

The problem seems to be connected with Nvidia proprietary drivers. From what I remember it didn't occur when the nouveau drivers were installed. Also it only affected the "hybrid graphics" mode (the "dynamic graphics" setting in the UEFI). The "discrete graphics" mode has another issue (brightness control does not work).

What finally has fixed it for me was the purge of all nvidia packages and the driver reinstallation.

$ sudo apt-get remove --purge '^nvidia-.*'
$ su
# for FILE in $(dpkg-divert --list | grep nvidia-470 | awk '{print $3}'); do dpkg-divert --remove $FILE; done
# exit
$ sudo apt-get install -f
$ sudo apt-get autoremove
$ sudo apt-get clean

After that reboot the system and install a proprietary Nvidia driver.

I hope this helps somebody.