It's difficult to discern the exact cause of the leaf loss. Since the photos are lower-resolution and can't get a magnified view, can you determine if the foliage in the interior is indeed growing off of this shrub's branches, or is perhaps a seedling that sprouted at the plant's base? It's not uncommon for resting birds to deposit weed seeds in their droppings, and those new plants can prosper even among the roots and branches of an existing shrub (and more likely to do so if that shrub is ailing). The green growth looks similar to Honeysuckle, but it's hard to tell.

Deer readily eat Euonymus foliage and have been known to strip plants they find palatable. Do they visit the yard, or have they been known to damage other plantings nearby? Similarly, a relatively new insect pest can also denude Euonymus in a fairly short amount of time. Have you seen these caterpillars around the plant recently?
Euonymus Leaf Notcher: https://extension.umd.edu/resource/euonymus-leaf-notcher

If the plant never leafed-out after winter, damage to its main stem(s) or root system would explain such widespread dieback. For plants intolerant of poor drainage, for instance, root flooding combined with compacted soil can deprive roots of too much oxygen. In that event, the overall damage is too great to expect reasonable recovery and the plant would need replacement. Alternatively, in the event of mere defoliation due to the above culprits, the plant should leaf-out again on its own shortly if it is otherwise healthy.

Only two, rarely-planted species of Euonymus are native to our region; the rest are non-native and can be invasive. If this is either Burning Bush or Manhattan/Japanese Euonymus, the most commonly used types, we recommend removing it. If this plant is already ailing for one reason or another, this is a good opportunity to replace it with a different species.
https://extension.umd.edu/resource/burning-bush

Miri

You're welcome.