I recently did a fresh install of Ubuntu 24.04 on an older computer from 2010 and the process was unexpectedly difficult. The system would completely freeze a few minutes after booting from a live USB drive; the only possible next step was a hard power off. This would happen on every boot, but the time between boot and freeze would be different for each attempt. No matter what I did, the freeze would always happen.
Luckily, I had encountered this issue before when I upgraded a different computer to Ubuntu 22.04. That time I was able to find the relevant error messages in my system logs (DMAR: DRHD: handling fault status reg 3) and search online for a solution: adding intel_iommu=igfx_off to the kernel command line (GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub). (I originally used intel_iommu=off but after some later testing found setting intel_iommu=igfx_off was enough.)
In the case of the live USB drive, I stopped the boot process at the Grub menu and added the same option to the kernel command line there. No freezes occurred in the current live session and I was able to complete the installation process. I also had to add the same option in /etc/default/grub to prevent the problem from occurring in the future.
When this happened earlier on a computer with an existing Ubuntu installation, I was able to boot with an older kernel, spot the error messages in the system logs, and find the solution online. With the live session, all logs are lost after powering off or restarting the system; it would have been very difficult to debug this issue in this situation.
I was able to resolve this issue relatively quickly due to prior knowledge and experience. I imagine if a Linux novice encountered this problem, at the very beginning of trying to install Ubuntu, they would have had no way to figure out what was wrong. Their only alternatives would be to try installing a different Linux distribution or to give up on Linux entirely.
Update: I believe Intel IOMMU is enabled by default in the 5.15 kernel and most modern distributions will leave it enabled, so I don’t think this issue is specific to Ubuntu. I have opened a bug in the kernel Bugzilla; I hope it can be resolved soon.