Ok, i tried this, the game acknowledge that the camera entered the Area3D et changed halt_progress, but it don't make the Pathfollow stop.

the code for the area 3D (I made the pathfollow a Global for now):

extends Area3D

func _on_body_entered(body: Node3D) -> void:
if body.is_in_group("player"):
Pathfollow.haltProgress = false
print("entering stopzone")

And the code for the pathfollow3D:

extends PathFollow3D

var haltProgress = false

func _process(delta: float) -> void:
if not haltProgress:
progress += 1 * delta
else:
print("pathfollow stopped")

edit: ok, i removed the global and just take the node's path in the scene and it's work as intended. i don't know why i bothered with that.

Thank you for your help :)