Dutch Iris (Iris hollandica) naturalize (multiply) over a short time. This can cause overcrowding and loss of vigor in the bulbs, which is why you saw less blooming this year – and they look exhausted. Every few years, bulbs can be dug up and culled out.

After digging them up, put them in cool spot away from the sun to dry them out a little for a few days. Keep the bulbs that are largest and healthy; toss the bulbs that are small, show signs of rot, are 'squishy', or have been damaged. Replant the best bulbs, usually about 12 bulbs per square foot.

If you still have healthy bulbs remaining, these can be given away to friends or neighbors, forced indoors, or just toss them. In CSU's Fact Sheet (below), it notes that if the even the best bulbs are not as large as the original ones planted, it would be best to purchase new ones.

CSU has information on fall-planted bulbs here:

https://extension.colostate.edu/topic-areas/yard-garden/fall-planted-bulbs-and-corms-7-410/