Inspect the shrub for sucking insects like aphids, spider mites, etc and apply a miticide or an insecticidal soap if pests are present. Since the leaves are cupping, ensure you are sufficiently irrigating as soon as the soil at a depth of 4" gets dry. Use enough water so the soil feels moist at a depth of 8 inches after waiting for the water to percolate down. Water the soil, not the leaves nor the blooms. Normal blooms: https://firsteditionsplants.com/product/berry-white-panicle-hydrangea/

Looks like simple drought stress to me.

@luis_pr @gardengal48 (PNW Z8/9) I was unable to find any insects on the hydrangeas. We had a lot of rain this summer, and I watered them twice a week using the irrigation system when there was no rain.

Maybe they are not getting as much water as you think? Since I am not there, I can't tell what rainfall, irrigation practices or soil conditions are or if extended high temperatures have been present but both the leaves and flowers show a very clear dryness or lack of water.

Test the soil moisture at a depth of 4 inches frequently when above 85F or if in a drought. As soon as it is dry, irrigate the soil directly (not the leaves nor the blooms) and deeply. Deeply means the soil should feel moist at a depth of about 8 inches after you irrigate and the water percolates down. If you irrigate and the soil is not moist at a depth of around 8 inches then you did not irrigate sufficiently. Maintain 3-4" or organic mulch up to the drip line so you can always keep the soil at a depth of 4" evenly moist.