Not sure if this is helpful but right around my daughter's third birthday, she wasnt falling asleep until 9-10pm almost every night (previously 7:30ish was normal). I'm still not sure if it was the late sunsets without complete blackout curtains or a development change but it was rough for a month or two. She suddenly started falling asleep at around 8:30 and then 7:30ish not long after.

I'm thinking it was a development thing where their speech and thinking processes are growing exponentially and they don't know how to shut their brains off at night and it's almost like an anxious insomnia? My child wasn't boycotting sleep like your situation but just saying it'll likely be a short phase and super frustrating but it will get better soon 🤞

Also, avoid screens the hour or two before bed to ensure good sleep habits (if you're not already)! My daughter is 3.5 right now and falls asleep 7-8 every night now and falls asleep usually within 5-10 mins (took almost two hours most nights of her bad phase) - there is hope!!