Button opens a door

Wire it

1. Draw a door sized brush in a doorway. Right click it, Create Brush Entity > func_door, and set its targetname to main_door in the Inspector. The default travel of 0 64 0 slides it up 64 units, 2 m.
2. Draw a small brush on the wall next to it and make it a func_button the same way.
3. Select both entities and choose Gameplay > Logic > Link Two Selected Entities.... The button must be on the left, press ⇄ if it is not. Pick pressed under When and open under call, then Link.

The status bar confirms the new output, pressed > main_door.open.

Let the player press it

The addon has no interaction system of its own. Doors and buttons have a use(activator) method and your player calls it. The demo player does it on E with a ray from the camera (godot/demo/player.gd):

func use_target() -> void:
    var from := camera.global_position
    var query := PhysicsRayQueryParameters3D.create(from, from - camera.global_basis.z * use_distance)
    query.exclude = [get_rid()]
    query.collide_with_areas = false
    var hit := get_world_3d().direct_space_state.intersect_ray(query)
    var node: Node = hit.get("collider")
    while node:
        if node.has_method(&"use"):
            node.call(&"use", self)
            return
        node = node.get_parent()

The player passes itself, so pressed(activator) carries the player and later outputs can target !activator.

Variations

The same wiring in code

# pressed(activator) > main_door.open
button.pressed.connect(func(activator):
    for door in GodotTrenchIO.find_targets(button, "main_door", activator):
        GodotTrenchIO.invoke(door, &"open", "", activator))

Connecting pressed straight to door.open fails, because pressed passes one argument and open() takes none. invoke fits the arguments to the method.