What problem does this feature solve?

是这样的，在我们的项目里遇到了问题就是，我们是基于vue的web components方案项目，但是对于某些组件来说，我们不希望它拥有隔绝样式的能力。 所以是否可以新增自由控制是否开启shadow-root

What does the proposed API look like?

defineCustomElement({
  shadowRoot?: Boolen
})

can you help me?

I believe this is linked to #4404 and #4314 . It would be nice if this was merged, currently the only way to bypass it is a "fix" that breaks slots

Any update on this？

Duplicate of https://github.com/vuejs/core/issues/4314