I'm on an AMD machine that System76 wrote the firmware for, and they specifically wrote in S3 sleep functionality despite the base firmware missing it.

Do you have a source for that? The only thing I've found is S3 sleep under coreboot, which only applies to intel.

These[1] have S3 sleep enabled in their firmware thanks to System76.

[1] https://hpdevone.com/

That's cool, but the 5850u is from 2021, around the time Microsoft started pushing hard for modern standby. Other laptops of that generation also have a S3 bios setting: https://www.reddit.com/r/GamingLaptops/comments/yvpae5/to_al...

The oldest AMD chip framework sells is two generations, and to me knowledge don't have S3 support.

Hopefully it can find it's way to Framework.

The firmware vendor contracted System76 to develop the feature specifically for Linux compatibility.

I'm unaware of how much access Framework has to the underlying firmware blobs. If they don't have source/license/keys/etc for the right parts, they might be at the mercy of their own vendors for S3 support.