There are likely several separate issues at work here. None are serious at this point and should be easily correctable over time.

The yellowing of the foliage while the veins remain green is a condition called chlorosis, and is a sign of malnutrition. This may be contributing to lack of bloom, but is probably not the key reason. It can be caused by a depletion of certain nutrients in the soil, but it can also result from a plant's roots dying back from oversaturation and rot, where they aren't functioning properly. For acid-loving plants like hydrangea, it can also result from a soil pH imbalance preventing the roots from absorbing plentiful nutrients in the soil. Only a soil test would reveal if soil deficiencies or a pH issue is the cause. If the plant is watered frequently (such as by automatic irrigation) or receives surplus water from a source like a roof downspout, only correcting this situation to allow it to remain drier will permit it to slowly recover and regrow roots. You shouldn't need to fertilize unless a soil test reveals a particular deficiency. Iron, manganese, and magnesium are the nutrients of interest when chlorosis manifests. pH changes are fairly simple to achieve, but do need months to gradually adjust acidity. Leaves that appear in future growing seasons that don't develop this pattern of yellowing will imply that the problem has been corrected.

The spots on the leaves are a common but relatively harmless fungal or bacterial infection. In years with severe infection, spots will be more numerous and could cause foliage to drop prematurely, but in most cases it's only an eyesore and does not need treatment. Avoid wetting the leaves often with irrigation  to lessen the chances of infection, though naturally rainy years may see higher infection rates naturally. You can clip off any particularly unsightly individual leaves if bothersome, but avoid stripping the plant of too many leaves as the rest of the tissue can still nourish it via photosynthesis.

Lack of bloom on this type of hydrangea tends to be caused by the loss of flower buds prior to bloom, though growing in deep shade may result in lack of flower production completely. They grow flower buds the summer and autumn prior to flowering, so this year's flowers (had they appeared) would have developed last summer/autumn. That means that these buds lie dormant on the stems all winter, even if they're not very prominent, and they can die due to an abnormal cold snap, be nibbled-off by deer, be trimmed-off by gardeners cutting back stems, or be killed after they start emerging from dormancy by a late winter warm spell followed by a hard freeze.

Accidentally trimming plants at the wrong time of year is a common cause; avoid trimming unless necessary to reduce the plant's size, and then do so only as the flowers start to fade (perhaps midsummer). Some modern varieties of hydrangea can continue to grow new flower buds in-season as a means to avoid these causes of flower loss, though they can only be identified as rebloomers by their variety names, since foliage will look identical to types that only bloom once. Lastly, so-called "florist" hydrangeas, varieties which are forced into early bloom, like for Easter-season sales as an indoor décor plant, aren't always cold-hardy enough to survive outdoors here and still flower, since flower buds tend to be a bit less hardy than foliage buds. Varieties in that category may never be reliable bloomers here, but planting them in a sheltered spot less prone to early-spring thaws or less exposed to the brunt of winter weather may allow them to be productive.

Miri