from collections import Counter

my_list = [{4, 8, 6, 1}, {6, 4, 1, 8}, {1, 2, 6, 2}, {1, 4, 2}, {7, 8, 9}]

print("The list is :")
print(my_list)
my_freq = Counter(frozenset(sub) for sub in my_list)

my_result = []
for key, value in my_freq.items():

   if value > 1 :
      my_result.append(key)

print("The result is :")
print(my_result)

The list is :
[{8, 1, 4, 6}, {8, 1, 4, 6}, {1, 2, 6}, {1, 2, 4}, {8, 9, 7}]
The result is :
[frozenset({8, 1, 4, 6})]