sendEmail: multiple recipients string?

Using sendEmail, how can I send an email to multiple comma-separated recipients by combining two form fields? It seems to work when (lastrow,4) has only one value (abc@domain.com) but not for more than one (abc@domain.com, xyz@domain.com). Current code is below, and the variable in question is recipientsTo.

function FormEmail() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheetform = ss.getSheetByName("Sheet1"); // Name of the sheet which contains the results
  var lastrow = sheetform.getLastRow();
  var recipientsTO = sheetform.getRange(lastrow,3).getValue() + "@domain.com";
  var recipientsCC = ""
  var team = sheetform.getRange(lastrow,5).getValue();
  var datestamp = Utilities.formatDate(sheetform.getRange(lastrow,1).getValue(), "GMT - 5", "yyyy-MM-dd");
  var html = "Intro text";
  
  //The questions order in the email will be the order of the column in the sheet   
    for (var i = 2; i < 11; ++i) {
    html = html + "<b>" + sheetform.getRange(1,i).getValue() + "</b><br>";
    html = html + sheetform.getRange(lastrow,i).getValue() + "</p><br>";
       }
   
  //Add additional emails if entered in form field
  if (sheetform.getRange(lastrow,4).getValue() !== "") {
    recipientsTO = recipientsTO + "," + sheetform.getRange(lastrow,4).getValue()
  }

  //CC if response to a question is "Yes"
  if (sheetform.getRange(lastrow,10).getValue() == "Yes") {
    recipientsCC = "ccEmaIL@gmail.com"
  }
  
   
  MailApp.sendEmail({
    to: recipientsTO,
    cc: recipientsCC,
    subject: "Subject",
    htmlBody: html,
});


}

According to the sendEmail(message) documentation, the TO field only has one recipient. Whereas the CC field can have multiple recipients separated by comma.

https://developers.google.com/apps-script/reference/mail/mail-app#sendEmail(Object)

`to - String - the address of the recipient.

cc -String - a comma separated list of email addresses to CC`

Another option would be to use sendEmail(String,String,String,Object) in that function "recipient String the addresses of the recipients, separated by commas".

Hope this helps.