This is a very common appearance for bigleaf hydrangea (Hydrangea macrophylla, this type of hydrangea) by late summer. Several kinds of leaf spots, caused by different fungi and bacteria, cause the maroon-brown spotting and subsequent holes in the leaves. Despite how drastic-looking or widespread the symptoms can be, these infections don't actually cause the plant too much harm overall.

If too great an eyesore, you can clip off individual leaves with the worst of the spotting, but don't cut the stems themselves back or you risk removing flower buds for next year's blooms (even though these buds aren't very prominent yet). No fungicide will be of use at this point, and even though applying one early in the season next year (and repeating several more applications for several weeks) might suppress disease, they are not foolproof measures and may risk negative impacts to pollinators and other organisms. This is why we typically don't recommend fungicides, not only because their application timing needs to be fairly precise and not interrupted by uncooperative weather to work well, but also because by the time symptoms are evident, the existing infection cannot be cured. (Fungicides are preventative measures only and can only protect healthy growth from infection.)

For the time being, you can just remove and dispose of the plant's fallen/withered leaves later this autumn or winter, because this could help reduce the likelihood they'll be infected early next season. Make sure that, if the plant needs irrigation during any dry spells in summer or autumn, that only the soil is watered; avoid wetting the leaves if possible. Otherwise, if you need to water in the summer and the foliage is going to get wet (like with a sprinkler), water early enough in the day so the foliage can be dry by nightfall, since wet leaf surfaces are more vulnerable to infection. Frequently-wet leaves could be the reason the cherrylaurel behind the hydrangea has shot hole disease, which itself is a very common but not debilitating infection they are vulnerable to. (This is similarly not easily or not very effectively treated with fungicides, so you can largely ignore those symptoms as well.) Many parts of Maryland have been fairly wet this summer from our deluge storms, so fungal outbreaks have been pretty commonplace. Fortunately, late-season leaf damage doesn't impact plants much because they've had all season to make and store carbohydrates to fuel the start of next year's growth.

Miri

You're welcome.