I updated my desktop to Ubuntu 24.04.1 LTS the other day. Although everything seemed fine, I was unable to get the system to suspend. Both from the command line (systemctl suspend) and the GUI, it would blank the screen and log me off but not suspend. Since it used to work, that was definitely something to do with the upgrade.
After searching around a bit based on the logged messages, I found a somewhat related bug. It wasn’t exactly the same thing, but got me thinking that the upgrade switched my video drivers.
When I went in to the additional drivers in the software and updates app, I saw that it had been switched from the proprietary driver to the Nouveau driver. I switched it back to the Nvidia 470 driver used before the update and rebooted. After that, suspend worked as before.
I’ll probably update the driver to a later version at some point, but I just wanted to be able to suspend the system for now.