final_array = array_camera.append(TD_camera)
final_direction = array_direction.append(TD_direction)

The above 2 lines doesn't work the way you expect.

append() function of list doesn't return anything. It adds data at the end of the list object through which the append() was called.

So final_array & final_direction will be None.

I think you just need to append data to final_array & final_direction. Like this

final_array ,final_direction =[],[]
.....
.....
final_array.append(TD_camera)
final_direction.append(TD_direction)

This post from stack overflow should give you what you want. The magic code boils down to the following.

flat_list = [item for sublist in l for item in sublist]

You can also loop through the list of lists and merge them.

lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

merged_list = []

for l in lists:
    merged_list += l

print(merged_list)
[1, 2, 3, 4, 5, 6, 7, 8, 9]

you want to stack them:

np.vstack(dat_list)

The json module only knows how to handle the basic Python types that it maps to the basic JSON types—list, dict, str, float, bool, and NoneType.

But you can override the JSON encoder and decoder objects to add in code to handle additional types in any way you want. This is documented, with some examples, but isn't entirely trivial.

But, more simply, if you know the structure of the data you're trying to save and load, you can just transform it on the fly. For example:

def save_stuff(f, list_of_arrays):
    list_of_lists = [list(arr) for arr in list_of_arrays]
    json.dump(f, list_of_lists)

def load_stuff(f):
    list_of_lists = json.load(f)
    list_of_arrays = [np.array(lst) for lst in list_of_lists]
    return list_of_arrays

Or you can go the opposite direction: convert the list of arrays to an array of arrays and use Numpy to save that.

Either way, this is less efficient, because you have to create those temporary lists. If you have gigantic arrays, or if you're doing this zillions of times, you will probably want to do the more complicated work of overriding the encoder and decoder.