Bedtime stalling has a shape, and the shape tells you what to fix
The requests that arrive after lights out look interchangeable. They are not, and treating them as one category is why bedtime advice so often fails to land.
Physical requests
Drink, toilet, too hot, too cold. These are largely solvable in advance, and mostly disappear once the routine includes them before the goodnight rather than after it.
Question requests
"What happens when the sun dies." Children's minds get quiet enough at bedtime for large thoughts to surface, frequently for the first time all day. Refusing to engage tends to prolong the episode; a short, honest, unhurried answer and a promise to continue tomorrow usually ends it.
Contact requests
One more hug, stay a bit, leave the door open. These are about separation and respond to predictability rather than to firmness — the same length of stay, every night, announced in advance, beats a negotiation that varies.
Identify which of the three you are getting before deciding what to do. The same response cannot be right for all of them.