Cynical take: so you buy it, then realize it's soldered, then buy another computer?
> But what I really want to know is where the full bios manual is, so that I can see if its possible to enable S3 standby.
Some Lenovo laptops that come with Windows have a "Sleep State" option that you can switch from "Windows 10" to "Linux", which I think is what disables Modern Standby? I've seen C3 be enabled by one of the options on a recent Lenovo, I think it was probably that setting.