Setting cookie's domain causes TypeError: option domain is invalid

Follow-up from Express session loses passport user ID on a Safari cookie every week . In Express and NodeJS, I want to set a cookie's domain so user agents see it as a first-party cookie. If I set it per the documentation:

const session = require('express-session');
const MongoDBStore = require('connect-mongodb-session')(session);
const express = require('express');
const app = express();
const max_session_ms = 365 * 24 * 60 * 60 * 1000;

app.use(
  session({
    cookie: {
      // Specifies how long the user's browser should keep their cookie, probably should match session expiration.
      maxAge: max_session_ms,
      sameSite: "lax",
      domain: "localhost:8080",
    },
    store: store,
    secret: some_secret,
    signed: true,
    resave: false,  // Unknown effect. See https://github.com/expressjs/session#resave
    saveUninitialized: false,  // Save only explicitly, e.g. when logging in.
    httpOnly: true,  // Don't let browser javascript access cookies.
    secure: false, // Only use cookies over https in production.
  })
);

then the domain is set in MongoDB:

> db.sessions.find().pretty()
[
  {
    _id: 'g6u-kuqpZDd28IyKkP4-dAfg8u7Mw_Tp',
    expires: ISODate('2026-02-25T09:09:34.210Z'),
    session: {
      cookie: {
        originalMaxAge: 31536000000,
        partitioned: null,
        priority: null,
        expires: ISODate('2026-02-25T09:09:34.210Z'),
        secure: null,
        httpOnly: true,
        domain: 'localhost:8080',
        path: '/',
        sameSite: 'lax'
      },
      flash: {}
    }
  }
]

but I get an error, coming from the modules and outside my own code, that prevents serving assets:

[2025-02-25T09:01:28.226Z] TypeError: option domain is invalid
    at Object.serialize (~/server/node_modules/cookie/index.js:217:13)
    at setcookie (~/server/node_modules/express-session/index.js:665:21)
    at ServerResponse.<anonymous> (~/server/node_modules/express-session/index.js:248:9)
    at ServerResponse.writeHead (~/server/node_modules/on-headers/index.js:35:16)
    at ServerResponse.writeHead (~/server/node_modules/on-headers/index.js:44:26)
    at ServerResponse._implicitHeader (node:_http_server:338:8)
    at writetop (~/server/node_modules/express-session/index.js:284:15)
    at ServerResponse.end (~/server/node_modules/express-session/index.js:351:16)
    at ServerResponse.send (~/server/node_modules/express/lib/response.js:232:10)
    at done (~/server/node_modules/express/lib/response.js:1045:10)

If I set the domain outside the cookie, i.e.:

app.use(
  session({
    cookie: {
      // Specifies how long the user's browser should keep their cookie, probably should match session expiration.
      maxAge: max_session_ms,
      sameSite: "lax",
    },
    domain: "localhost:8080",
    store: store,
    secret: some_secret,
    signed: true,
    resave: false,  // Unknown effect. See https://github.com/expressjs/session#resave
    saveUninitialized: false,  // Save only explicitly, e.g. when logging in.
    httpOnly: true,  // Don't let browser javascript access cookies.
    secure: false, // Only use cookies over https in production.
  })
);

then I don't get the error, but the MongoDB database does not store the domain of the cookie:

> db.sessions.find().pretty()
[
  {
    _id: 'ibvlIGHwATOV1siRT4NB-a2AhzhyZL68',
    expires: ISODate('2026-02-25T09:07:13.289Z'),
    session: {
      cookie: {
        originalMaxAge: 31536000000,
        partitioned: null,
        priority: null,
        expires: ISODate('2026-02-25T09:07:13.289Z'),
        secure: null,
        httpOnly: true,
        domain: null,
        path: '/',
        sameSite: 'lax'
      },
      flash: {}
    }
  }
]

How can I set a cookie's domain in NodeJS and Express? Or how can I debug the error coming from outside my own code?