After a software update Ubuntu asked me to restart it. Instead I shut it down, because I had to leave. On the next start attempt the start freezes without a real error (there is a standard message that pops up on every system start, but nothing new).

I can still (fully) boot in recovery mode. I tried the fix dpkg option and check disks, but that didn't change the result.

I had the same problem about a month ago after trying to install CUDA drivers manually - because the automatic installation failed. It was the exact same freeze, but because I see no error message, it could be something else of course. I fixed this error by reverting the manual changes (I don't remember what I did exactly). I have updated software before in that time period so I don't know whether it could actually be still from that.

I should mention that I run a dual boot where Ubuntu is the default starting os. I didn't boot windows inbetween (shutting linux down and restarting it).

I am unsure how to debug this problem further.

Message

The message shown - but as far as I know it has always been shown - is:

[2.268282] pcieport 0000:00:1c.0: pciehp: Cannot get irq -1 for the hotplug controller
[2.268289] pcieport 0000:00:1c.0: pciehp: Notification initialization failed (-1)
/dev/nvme0n1p5: clean, 782387/67428352 files, 26148817/269699840 blocks

Startup

1. Grub appears. I select Ubuntu
2. Initial message appears and system freezes
3. I shut it down by pressing the Off-Button (just once not a kill)

Attempted Solutions

Reinstalling Grub

Following these steps: https://www.maketecheasier.com/restore-grub-2-as-the-main-bootloader/ while being in recovery mode:

sudo fdisk -l | grep "Linux" only finds /dev/nvme0n1p5 ... Linux filesystem. After mounting that sudo mount /dev/nvme0n1p5 /mnt and checking that it actually contains files (as expected bin dev home lib64 media proc sbin swapfile usr boot etc lib libx32 mnt root snap sys var cdrom grub lib32 lost+found opt run srv tmp) the installation sudo grub-install --force --boot-directory=/mnt/ /dev/nvme0n1p5 fails with:

Installing for x86_64-efi platform.
grub-install: error: cannot find EFI directory.

I checked and fdisk -l doesn't contain a /dev/sda1 entry.

I also tried updating grub despite the failing of the installation which works without any issues.

The problem persists.