threshold = [0.97, 0.9, 0.83, 0.6]
my_list = [[3, 0.99, 1], [2, 0.98, 54], [10, 0.85, 4], [1, 0.7, 10], [12, 
    0.69, 31], [12, 0.65, 43], [1, 0.56, 0]]
threshold = [0.97, 0.9, 0.83, 0.6]
index_list = []
ti = 0
for i, item in enumerate(my_list):
    if item[1] >= threshold[ti]:
        continue
while ti < len(threshold) and item[1] < threshold[ti]:
    index_list.append(i)
ti += 1
Python: index of fist element smaller than threshold in reverse sorted list