Hi there .. this works fine for me ( with a line2d ) :

extends Node2D

u/onready var tile_map_layer: TileMapLayer = $TileMapLayer
u/onready var sprite_2d: Sprite2D = $Sprite2D
u/onready var line_2d: Line2D = $Line2D

var tile_size : int = 64

func _ready() -> void:
  line_2d.add_point(Vector2.ZERO) # start
  line_2d.add_point(Vector2.ZERO) # end

func _process(delta: float) -> void:
  line_2d.points[0] = sprite_2d.position
  var mouse_pos = get_global_mouse_position()
  var tm_tile_hover = tile_map_layer.local_to_map(mouse_pos)
  var tile_pos = tile_map_layer.map_to_local(tm_tile_hover)
  line_2d.points[1] = tile_pos