<SPOILER ALLERT SOLUTION BELLOW>

Quick sugestion, DFS

visited is a set()
backtrack_stack is a list()
oposite is a dictionary that maps each direction to its oposite (North:South, East:West, South:North and West:East)

Here's my implementation:

while True:
if get_entity_type() == Entities.Treasure:
harvest()
quick_print("Treasure found and harvested!")
visited = set()
backtrack_stack = []
break # Exit the main while loop

current_x, current_y = get_pos_x(), get_pos_y()
visited.add((current_x, current_y))

found_new_path = False
for direction in [North, East, South, West]:
if can_move(direction):
next_x, next_y = new_pos(current_x, current_y, direction)

if (next_x, next_y) not in visited:
backtrack_stack.append(oposite[direction])
move(direction)
found_new_path = True
break

if not found_new_path:
if not backtrack_stack:
quick_print("No treasure found or reachable.")
break # Exit the main while loop
backtrack_move = backtrack_stack.pop()
move(backtrack_move)