My Framework seems to get worse battery life on Linux than Windows. Different tools like powertop help close the gap, but inevitably if I put the framework in a bag for a week, it'll be dead when I take it out
I shut mine down completely and haven't had the battery drain issue, but on "modern standby," yes these don't last very long. Probably 2-3% per hour on standby and worse than that if anything is plugged into the expansion slots.
If you're going to put it in a bag for a week, why not use some kind of hibernation feature?
If your laptop is using a recent AMD Ryzen based SoC:
ACPI C4 power state (for powering down more of the SoC during S0ix suspend) is not supported on Linux yet, for recent (last couple years) AMD processors.
Patches submitted for 6.18 were described as "laying the foundation for AMD C4 support". So, maybe won't be fully supported until 6.19 or even later; Sorry, I haven't followed up to see what has actually landed.