Sleep Training culture is full of misinformation.
Firstly, you can't train sleep, sleep is a biological function that we do in the womb.
Secondly, self settling isn't possible for a young infant because the brain pathways required for this aren't even developed yet.
So, those who have sleep trained haven't magically taught their child to "self settle" or link cycled, they have merely used a behaviour modification technique (all of which require the caregiver to limit their responses to the child - even those sneakily marketed as "gentle") and therefore teach the child that, that need, will not be met by their caregiver so they essentially give up trying to conserve energy. They still wake, research has shown this, and they are still distressed, it's just they have been trained not to call out for that need, and in some circumstances they don't bother calling out at all, there's been plenty of sleep trained babies who have been sick in the night but didn't call out for help, then parents are going into the room in the morning and there's vomit in the cot.
Infant sleep can be such a minefield especially as sleep training culture is shoved down our throats, which isn't evidence based and is potentially detrimental to our children's emotional development.
BASIS is a great evidence based resource thar has great information on normal baby sleep and the potential costs of sleep training.
They are all individuals and baby sleep isn't linear.