When a run npx create-nuxt-app, it skipped the custom server framework option to UI framework. It was not mention on nuxt release note as well.

It was mentioned in the release note for v3.0.0, particularly PR #501.
From my understanding, they just wanted to move it to separate server templates instead of including it out of the box in this create-nuxt-app. You can read about the serverMiddleware which is the recommended approach going forward if I'm not mistaken.
You can read more about the reasoning and links to the server templates like Express, Koa, Adonis etc over at this comment in #563. Feel free to forward your questions over there since it should be the open issue for this type of question.
I need select koa2 options!
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It was mentioned in the release note for v3.0.0, particularly PR #501.
From my understanding, they just wanted to move it to separate server templates instead of including it out of the box in this create-nuxt-app. You can read about the serverMiddleware which is the recommended approach going forward if I'm not mistaken.
You can read more about the reasoning and links to the server templates like Express, Koa, Adonis etc over at this comment in #563. Feel free to forward your questions over there since it should be the open issue for this type of question.