> not possible to apply in all situations (array in map in array).

Yes, that's largely why inline tables and arrays exist:

   >>> tomllib.loads("""
   ... [[outer]]
   ... first = [1, 2, 3]
   ... second = [4, 5, 6]
   ... 
   ... [[outer]]
   ... third = [7, 8, 9]
   ... fourth = [10, 11, 12]
   ... """)
   {'outer': [{'first': [1, 2, 3], 'second': [4, 5, 6]}, {'third': [7, 8, 9], 'fourth': [10, 11, 12]}]}