at what age does it feel effortless or instinctive to potty train a toddler ?

I’ve heard 3 years old is the magic age even though some kids are ready earlier.

Depends on what you mean by effortless/instinctive. I potty trained my son at 26mo which felt overall pretty easy but it did require effort for the first week

My daughter was 2 years 10 months old, I didn’t have to ‘train’ at all. She had 3 accidents the first day, 2 the second day and none after that, there was no need for timers, rewards, constantly putting her on the potty, days spent at home etc etc. Purely because she was developmentally old enough to hold her bladder, understand the expectation and wanted to be a ‘big girl’ and not have nappies. My friend has had similar experiences waiting until her children are nearly 3, I personally don’t understand why people start so early then have months and months of it when you can wait and have it done in days.

I think it depends on when the child is ready. We’ve tried when she was 2.5yo and the first day was a breeze, but then she started holding her pee for too long until she wasn’t able to (I’m talking more than 12hrs) and we went into a power struggle because I needed her to pee (holding pee for too long can cause kidney damage, infections etc) and we weren’t going anywhere. Talking with her nursery teachers and HV, they told me to just wait until she was emotionally ready. Now she’s literally saying “I’m not a big girl, I want my nappy” so I guess she’s still not ready. It also depends on your child temperament, some adapt really well to changes so it’s easier for them do it even if they’re not 100% ready, some don’t (mine struggles really badly to any minor change).