First there is no difference between having several lists or one long list, so merge all lists into one
biglist = list1 + list2 + list3
Then you can determine the number of subplots needed from the length of the list. In the simplest case make a square grid,
n = int(np.ceil(np.sqrt(len(biglist))))
fig, axes = plt.subplots(n,n)
Fill the grid with your images,
for i, image in enumerate(biglist):
axes.flatten()[i].imshow(image)
For the rest of the axes turn the spines off
while i < n*n:
axes.flatten()[i].axis("off")
i += 1