Big leaf hydrangeas, like endless summer, and mountain hydrangeas, like Tuff Stuff, should not be pruned. There are flower buds on the woody stems that have to survive the winter. They often don’t in the Midwest. Plant these in a location where they can grow to their full size and not require pruning. When the flowers come out and the leaves come out, you can go in and take out any dead stems and remove them completely. there is very neutral or even basic pH soil here in the Midwest. These types

This is a big leaf/macrophylla hydrangea. If you’re fortunate enough to have them bloom(🤣😭!), you may have a different problem, which is that they sometimes outgrow their space. You can move and divide these if needed. When? You can do this any time the ground’s not frozen, including when they’re in bloom if necessary. It’s important not to prune these otherwise no because you could be cutting off the buds that will turn into flowers. (Is your not blooming at all? Just get an oakleaf hydrangea