1 Easy but re-render

most simple way, but it will re-render. It may be related to the scrolling restoration bug when the user return the page if your data is fetched on the client

import {useState, useEffect} from 'react'

export default function Index() {
  const [mounted, setMounted] = useState(false);
  useEffect(() => {
      setMounted(true)
  }, [])
  
  return mounted && <div>Run on client only</div>
}

2 Best way.

Fixed scroll restoration bugs and re-render problem. but I have to use it with Jotai - state management. You can also use it with other state management.

state.tsx

export const mountedAtom = atom(false)

useMounted.tsx

import { useEffect } from "react"
import { useAtom } from "jotai" // 2.2KB gzip
import { mountedAtom } from "state" // import from state.tsx

export default function useMounted() {
  const [mounted, setMounted] = useAtom(mountedAtom)
  useEffect(() => {
    if (!mounted) setMounted(true)
  })

  return mounted
}

How you use it:

  const mounted = useMounted()

meotimdihia/How to fix the bug: "Warning: Expected server HTML to contain a matching <div> in <div>." in Next.js.md

1 Easy but re-render

2 Best way.