const Discord = require("discord.js");
const bot = new Discord.Client();
const prefix ='!';
require("dotenv").config();




bot.on('message' , message => {
  if (message.content.startsWith('!check')) {

    const list = bot.guilds.cache.get("708789786579828736");

    list.guild.members.forEach(member => console.log(member.user.username));

    if (member) {
      for (user of list.members) {
        console.log(user[1].username);
      }
    }

  }
})

您可以尝试这个吗？

无法读取未定义的属性'members'>>

const Discord = require("discord.js");
const bot = new Discord.Client();
const prefix ='!';
require("dotenv").config();




bot.on('message' , message => {
  if (message.content.startsWith('!check')) {

    const list = bot.guilds.cache.get("708789786579828736");

    list.guild.members.forEach(member => console.log(member.user.username));

    if (member) {
      for (user of list.members) {
        console.log(user[1].username);
      }
    }

  }
})