Например так:
Python 3.12.4 (main, Jun 6 2024, 18:26:44) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> initial_data = {
... "coords": [[673, 103], [673, 104], [673, 105], [673, 104]]
... }
>>>
>>> transformed_data = {
... "coords": [{"x": coord[0], "y": coord[1]} for coord in initial_data["coords"]]
... }
>>> transformed_data
{'coords': [{'x': 673, 'y': 103}, {'x': 673, 'y': 104}, {'x': 673, 'y': 105}, {'x': 673, 'y': 104}]}
>>>
