If you are using Godot, probably the best way would be using a state machine and creating a state for "cinematic" or "dialogue" where the character doesnt respond to movement input. A quick one that I have used is making a bool variable, lets say "is_in_dialogue" or "is_alive", and then nest all movement code inside an -if- statement that checks for that variable. Then, in the function that triggers the dialogue, you change the bool. When the dialogue is completed, you change it again. This  works easily if all your movement is inside the _physics_process

Dont worry about it, I saw nothing xD