I have a Thinkpad X1 from 2018 and by default it came with S0ix enabled and Lenovo later on added the S3 sleep state option through a BIOS update, called "Linux compatibility something".. Before that, one had to manually edit the DSD table to get rid of this evil burning-sleeping-laptop-in-backpack-feature called S0ix.

Does the Framework Laptop, or other popular models from the other manfacturers you mentioned, not have a S3 sleep state option these days, i.e. S0ix only?

S0ix has stronger requirements on the "correct" interaction between firmware/BIOS and OS, it offloads more work to the OS. Poorly implemented S0ix will drain the battery faster, but correctly implemented S0ix is as good as S3 or even better.

Lenovo put out a buggy S3 implementation on some systems that hasn't been tested well because it's only an optional "Linux suspend" setting. Drains twice as fast as Linux with correctly implemented S0ix. And the worst thing is, nobody except Lenovo do can fix it because it's all on the BIOS level, and their China-based firmware team has other priorities.

Well-implemented S3 is nice. But it's going to disappear. Both Intel and AMD are switching away with full force, vendors won't have S3 options in the BIOS going forward and the ones that remain will likely suck. On the other hand, S0ix support is coming together even on AMD platforms which were a little late to the party. Once it's working decently, I'd rather trust my OS than my laptop manufacturer's firmware team to suspend components correctly.

Isn't secure boot just a Microsoft thing to try to stymie competition by preventing booting OSes other than Windows?