print(pd.__version__)
jsn={'_id':{'a1':10,"l2":{"l3":0}}, "gg":4}
display(pd.json_normalize(jsn,sep='_'))

Actual result:

1.5.2
  gg | id_a1 | id_l2_l3 -- | -- | -- 4 | 10 | 0

Expected result: the "_" prefix should not be removed from the beginning of the column names.

1.5.2
  gg | _id_a1 | _id_l2_l3 -- | -- | -- 4 | 10 | 0

This issue was introduced with the following change: https://github.com/pandas-dev/pandas/pull/40035/files

Comment From: iyonchev

display(pd.json_normalize(jsn,sep='_', max_level=5)) passing max_level value could be used to prevent the execution of the new methods(from the change above) and execute the main one...

Comment From: jbrockmendel

Cc @WillAyd