Redstone dust updating has changed in 1.20, and redstone dust is also redirected by dust on an open trapdoor.

reproduce:

part 1: build the contraption in attachment in 1.19.4 and 1.20, placing the dust on the trapdoor last. You won't be able to place the redstone dust on the trapdoor in 1.20.

Part 2: Build the redstone line in 1.19.4 and 1.20. the redstone goes straight in 1.19.4 when you open the trapdoor while in 1.20 the redstone stays curved.