Unfortunately, the photos are too small for us to enlarge to get a good look at its symptoms. The trunk color and texture doesn't look like a white birch, but it's hard to tell for sure. Are you able to get close-ups of (green) foliage and the bark? Might this be another type of birch instead, or a hornbeam (which looks very birch-like in its foliage)?

If this is a white-barked birch, they are rarely planted in our area due to a poor intolerance for hot weather. This easily stresses them, especially coupled with drier conditions, and stress makes them more vulnerable targets for attack by pests or disease, namely the native insect Bronze Birch Borer. Our locally-native river birch is resistant to that pest. Borers like this can cause branch dieback as they damage the sapwood which keeps branches and foliage alive. Look for signs of emergence holes about 4-5 millimeters wide near dead wood or sparse growth. For this beetle they will be in the shape of a D - that is, roughly circular but with one flatter side.

Regardless of whether or not this is a birch, the tree may be stressed for water depending on how much rainfall the decking blocks from its root system. Assuming the deck gap for its trunk isn't touching the bark, and that no cleaning or other chemical treatment of the deck occurred in the past few months, other environmental factors are likely at work. Fertilizer isn't recommended, but irrigating the root zone may be useful if the soil feels fairly dry several inches beneath the surface.

Some of the branch tip browning and dropping may simply be due to periodical cicada egg-laying damage. Look for wounds on the twigs that look like a dashed line of tears or cuts into the bark. When this is the cause of branch tip dieback, no action needs to be taken and the tree won't suffer negative health impacts. It is possible that this plus unrelated other issues are impacting the tree at the same time, however. The decline of the canopy, where branch death is patchy and foliage is off-color and smaller than usual, suggests something other than just cicada and drought damage is at work.

You may want to have a certified arborist assess the tree, especially since they will be able to see more detail regarding its current status and growing conditions. You can use the link below to search for a credentialed arborist; some work as members of a tree care company while others work independently.
https://www.treesaregood.org/findanarborist/arboristsearch

Miri