Apologies for the confusion. FydeOS at this moment does not support hibernation(S4 state), yet.
In previous FydeOS releases for Surface range, there was a kernel issue preventing the system to properly recover from sleep (S3 state). We have fixed the issue in 12.1, therefore Surface Go can now go into S3 state and fully recover without issue. But like you mentioned, 5% drain during S3 state is somewhat too high compare to S4.
Here is how Chromium OS manages its power and invokes power-saving mode (In Chromium OS terminology it’s “Suspend”):
As you can see, by design, the device will go “shutdown” once suspended.
In the “Configuring suspend mode” section the document mentioned
suspend_mode preference only has
deep option, per power states doc it does not support S4 “disk” mode.