I am having an issue with TypeScript and express-jwt

Your code has two problems:

1. getToken should return a string or undefined (the signature is: TokenGetter = (req: express.Request) => string | Promise<string> | undefined;), and req.query returns ParsedQs, so you need to make sure req.query.token is a string, for example:

return req.query.token as string; // or implement string validation

2. your options is missing now required algorithms parameter.

Try the full code:

static loginRequired() {

    expressjwt({
        secret: process.env.SECRET,
        credentialsRequired: true,
        getToken: function fromHeaderOrQuerystring(req: Request) {
            if (req.headers.authorization && req.headers.authorization.split(' ')[0] === 'Bearer') {
                return req.headers.authorization.split(' ')[1];
            } else if (req.query && req.query.token) {
                return req.query.token as string; // or implement string validation
            }
            return null;
        },
        // required
        algorithms: ['HS256'] //supported algorithms: https://github.com/auth0/node-jsonwebtoken#algorithms-supported
    });
}

see: express-jwt API

The error happens because newer versions of express-jwt require getToken to return only a string or Promise<string>.

But req.query.token in Express can be string | string[] | ParsedQs | ParsedQs[], so TypeScript won’t accept it.

You just need to narrow the query value to ensure you return only a string:

import { expressjwt } from "express-jwt";
import { Request } from "express";

class Authentication {
  static loginRequired() {
    return expressjwt({
      secret: process.env.SECRET as string,
      credentialsRequired: true,
      getToken: (req: Request) => {
        if (
          req.headers.authorization &&
          req.headers.authorization.startsWith("Bearer ")
        ) {
          return req.headers.authorization.split(" ")[1];
        }

        const token = req.query.token;

        // Only return a string to satisfy TokenGetter
        if (typeof token === "string") {
          return token;
        }

        return null;
      },
    });
  }
}

export { Authentication as auth };

Why this fixes it:
By checking typeof token === "string", you guarantee the function returns a valid type (string | null).
The older version you wrote years ago worked because express-jwt had looser typings; the newer typings are stricter.