Discord.js not capturing name after !register command

    if (message.content === '!registrar') {
        // pegue o nome do usuário digitado após o comando "!registrar"
        var newName = message.content.split(' ')[1];
        console.log(newName);
    }

The idea is to capture what the user types after the !register and store it in the newName variable and display it in the console for testing, but it is not storing it and it also does not print any results in the console, nor does it print the message "undefined", it seems to me that the split is not working, however when I put only message.content without the split also it does not store what was typed by the user.

I tried to store in the variable only what the user typed without using split and it still didn't store it, I also tried to just show that the command is working after trying to store the information in the variable but it also doesn't go to the next line, it doesn't display no errors in the console, it just doesn't display what the user typed after the "!register"

In your if condition you check if the message equals '!registrar'. It won't work with a command like '!registrar Name'.
You need to check if the entered String starts with the given command prefix.

So you have to change it like that:

const registerCmd = '!registrar';
// check if message starts with register command
if(message.content.startsWith(registerCmd)) {
  // get name from message
  let args = message.content.slice(registerCmd.length).trim().split(/ +/g);
  let newName = args.shift().toLowerCase();
  // print name
  console.log(newName);
}

For more information check the docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith?retiredLocale=en