Q.How Do I Keep My Strawberry Hydrangea From Getting So Tall That It Falls Over?
I prune it back in the fall and it grows so tall that by august the flower is so big that the stems can’t support it and they droop over.

Certified GKH Gardening Expert
The stems typically are sturdy enough to hold the boughs. If you wait till spring to prune, just before new growth starts, I believe the stems will be sturdier. Cut it back at least by a third. In your zone, they should be planted in full sun and they do not need much fertilizer, just a handful of slow release in spring, or compost added in spring. Be sure it isn't getting too much fertilizer. None is better than too much.
I can't tell if it is in the ground or in a container. Either way it needs well-draining soil. In a container, make sure it is large enough to accommodate the roots and has adequate drainage holes.
This article should help:
https://www.gardeningknowhow.com/ornamental/hydrangea/panicle-hydrangea-care

