@amayasasaki I have the secret for you. The problem is you are catering in some way shape or form. Your child is seeking your attention typically, that is part of what makes us love them so much - they just love us that much. So anything he can do to prolong bedtime is rewarded with more attention.
I know this well, I willingly fall for at least an hour of it every night. I work all day, I get so little time with them and it’s full of cuddles.
My wife has a different method, she is more no nonsense. She sees them all day long and she wants to be in bed asap - she’s spent.
My wife can do one story, a kiss, and she’s out. I cannot, if I do she will cry and find every excuse in the book to talk to me. And come out of her room, ask me to get books, anything. Frankly her guise is transparent.
The difference is my wife set the expectation, and stuck to it. Now my wife (and I) paid a price in dealing with short term my daughter went through- lots of crying and screaming. But only for a short while.
My wife was able to maintain the routine just short and sweet. I was not, I caved so early because I also wanted her attention in a 1:1 every day, I love it.
That the secret, set the rule, suffer for a short period, and be consistent.
I would recommend finding a balance between the max 2 stories, one song, and some snugging and light chit chat that I do, and the straight to bed that she does. that way you can both maintain it.