While we cannot see enough detail in the images to determine the core cause of the holly's defoliation, it may not be critical in this case as it would be best to replace the plant instead of attempting treatment. This size of its trunk indicates this is not a compact-growing variety of holly and the size to which it is currently being maintained (presumably due to how close it is to the driveway and light fixture) is too small for it to remain aesthetically pleasing and in good health long-term. While hollies do respond quite well to trimming in general, this degree of size reduction is likely causing it stress.

Secondary issues - perhaps scale insects (see link below) - are also likely contributing to its inability to maintain a dense outer layer of foliage. Evergreens routinely shed a small amount of old foliage each year (for hollies, this happens in spring), but this usually coincides with new growth on the branch tips. When those tips are removed by annual shearing, the plant loses some ability to remain dense and leafy. If a pest outbreak or drought stress overlaps with this phenomenon, that will further hamper its ability to replace those lost leaves.
https://extension.umd.edu/resource/soft-scales-trees-and-shrubs

This looks like it might be in the "blue" holly group (a variety of Ilex x meserveae), but there are dozens of holly hybrids which look nearly identical. Regardless, it is too large-maturing for the location it was planted, though you could replace it with a smaller-growing variety if you wish to keep a holly here. Other evergreens are also alternatives, though choices will depend on growing conditions. While no plant will be pest- or disease-proof, usually major problems don't arise unless a plant is first stressed by environmental conditions. In this location, keep in mind the driveway will restrict some root spread and the house wall may reflect some added heat during summer. Siting the planting hole for a future shrub a bit further into the yard - both away from the driveway and away from the house wall - may help by giving it more room to mature unimpeded.

If you instead wish to keep the plant and treat it, look for signs of scale based on information in the pages linked above and below. Neem oil isn't the ideal treatment option for scale, and any spray used would need to be re-applied several times a week or two apart in order to gain control over the population. (As with any pesticide, follow label instructions for the details on timing.) Thorough coverage of leaf undersides is critical when spraying for scale on hollies. Equally important is monitoring the plant for crawlers, which is the life stage of greatest vulnerability. One way to do this is to wrap a few stems in double-sided tape and inspect it once or twice a week for crawlers which have gotten stuck. This indicates when sprays will be most effective to apply. For the scale most common to holly, named Cottony Camellia Scale, crawler emergence tends to occur in June: https://extension.umd.edu/resource/cottony-camellia-scale-shrubs

Spiders are harmless to plants and beneficial in gardens. If you are instead thinking of spider mites, yes, they can be pests and can be controlled with neem oil, but they are not typical pests of holly and we don't see evidence of a population in the photos.

Since we are expecting hot weather soon, avoid spraying during temperatures above 85 degrees, or else you risk damaging the foliage.

Miri

Miri,

Thank you for the detailed response.

This is helpful.

You're welcome.