Suspending and Resuming Thinkpad X1 Carbon Gen 10 in Debian 12

S3 suspend used to work on this machine, but then I updated the firmware and now it doesn't. systemctl suspend makes the screen go black and print > Allocating and mlocking memory: 1050624 kb > Sleeping ... And that's it. It just hangs there. I updated the firmware to fix a different, but probably worse bug where the system would not boot if a usb device was inserted. What I've done to try to fix it: - Reinstall firmware via gnome-firmware - Upgrade to kernel 6.7 (from bookworm-backports). - Use S0 sleep instead of S3 (which worked before). Help will be much appreciated! I travel a lot and sleep mode is very convenient! Update: I got it working. See answer below.