Since next.js does not have built-in solutions for active link styling, I spent some time looking for a concise way so implement it. This is the best one I've found so far. The code is written in typescript, but you can delete the types if you don't want to bother with the types.

How to Use it

Just replace Links with NavLink and pass in activeClassName as a prop and style the link with whatever activeClassName is.

import React from 'react'
import Link from 'next/link'
import { useRouter } from 'next/router'

type Props = {
    href: string;
    children: any;
    activeClassName: string;
}

const NavLink =  ({ href, children, activeClassName}: Props) => {
  const router = useRouter()
  let className = children.props.className || ''
  if (router.pathname === href) {
    className = `${className} ${activeClassName}`
  }

  return <Link href={href}>{React.cloneElement(children, { className })}</Link>
}

NavLink.defaultProps = {
    activeClassName: 'selected'
} as Partial<Props>

export default NavLink

Example:

<Link to="/" activeClassName="activeLink">Hello</Link>