mylist = [{"a": 1, "b": {"c": 2, "d":3}}, {"a": 3, "b": {"c": 4, "d":3}}]

import pandas as pd

result_dataframe = pd.DataFrame(mylist)
print(result_dataframe)

a   b
  0 1   {'c': 2, 'd': 3}
  1 3   {'c': 4, 'd': 3}

new_dataframe = result_dataframe.drop(columns=["b"])
b_dict_list = [document["b"] for document in mylist]
b_df = pd.DataFrame(b_dict_list)
frames = [new_dataframe, b_df]
total_frame = pd.concat(frames, axis=1)

a   c   d
0   1   2   3
1   3   4   3