I have a ThinkPad X1 Carbon gen 10. If I boot it up with the USB-C power cable connected, and then unplug the cable, the laptop shuts down within a few seconds of unplugging the cable.
I’ve disabled the power management settings in the BIOS. I set suspend mode to Linux S3 in the BIOS, but it shouldn’t be attempting suspend anyway, as I have that set to 15 minutes on battery before suspend.