FWIW, and understanding that individual babies do differ, most babies can sleep through the night (10-12 hours) by 3-4 months old. Check out the books "Twelve Hours' Sleep by Twelve Weeks Old" or "Precious Little Sleep" for guidance.
In my case where n=2, naps during the day are/were not all that consistent but at night (unless they are very sick or something) the kids sleep.
I’m convinced that 1 of 100 babies sleeps miraculously, magically, the true sleep of the just, right out of the box. Some lucky parents of those genetic freaks think, “Our sleep technique works! We should write a book!”
Yeah. My wife was breastfeeding and she could do that half-asleep. Barely any sleep was lost.
3 for 3 sleeping through the night by 60 days. All we did was have a feeding schedule that we stuck to pretty closely, and around week 2 started intentionally delaying our response to night-time crying, gradually increasing how far we stretched it (start with maybe a minute, increase over time). They wake up at night and don’t know how to self-soothe back to sleep if you always jump in the second they make a sound, they don’t actually need night time feedings past the first few weeks, responding immediately trains them not to fall back asleep on their own if they stir at night (and everyone does). Down to one feeding at night by a month or so, none past two months.
Can’t say many other things worked equally well for all three kids, but that did.