To handle deep reactivity in nested objects without impacting performance in Vue 3, it's important to avoid observing more data than necessary. I typically use reactive() for complex states and ref() for specific values, combining them with computed to efficiently derive information. When working with very large structures, it's advisable to divide the state into smaller modules, use shallowRef() or shallowReactive() when deep reactivity isn't required, and minimize the use of deep deep watchers , as they can incur a significant cost in large-scale applications.