服务器端代码需要等到代码加载到浏览器中后才能使用浏览器API。
Vanilla js服务器端兼容

const [isMounted, setMounted] = useState(false);
  
useEffect(() => {
 if (isMounted) {
  console.log('hash', window.location.hash);
 } else {
  setMounted(true);
 }
}, [isMounted]);

if(!isMounted) return <>Loading...</>;

使用next/router

import { useRouter } from 'next/router';

const { asPath } = useRouter();

useEffect(()=>{
 const hash = asPath.split('#')[1];
}, [ asPath ]);

FYI你的代码不应该返回零。第一个出现在脑海中的罪魁祸首是当一个速记条件被使用而没有一个else。

window && window.location.hash

这应该有一个else

(window && window.location.hash) || null

或

window && window.location.hash ? window.location.hash : null

扩展@Sean W的答案，如果你想从一个哈希键中得到一个特定的哈希值，you can use URLSearchParams：

// example path: /#error=unauthorized_client&error_code=401error_description=Something+went+wrong

import { useRouter } from 'next/router';

const { asPath } = useRouter();

useEffect(() => {
  const hash = (asPath as string).split("#")[1]; // error=unauthorized_client&error_code=401error_description=Something+went+wrong
  const parsedHash = new URLSearchParams(hash);
  const errorHash = parsedHash.get("error_description"); // Something went wrong
}, []); // `asPath` omitted from dependencies as ESLint states it won't change