Couldn’t tell you unfortunately. It looks like AMD is also on board with deprecating S3 sleep, so I would guess that it’s not significantly better. The kernel controls the newer standby modes, so it’s really going to depend on how well it’s supported there.
Not in general, sorry. Best bet is to make sure you’re using the most recent kernel, which Ubuntu tends to lag on. You can also try checking out the arch wiki entry for it. It’s a different distro, but the wiki is good and commonly has tips relevant for any distro.