If you call the formatDate function you have in your code, I believe that will get rid of the timezone information.

var startDate = new Date("1990-01-01"); //YYYY-MM-DD
var endDate = new Date("2022-01-01"); //YYYY-MM-DD

function formatDate(date) {
  const year = date.getFullYear();
  /* getMonth returns dates from 0, so add one */
  const month = date.getMonth() + 1;
  const day = date.getDate();
  
  return `${year}-${month < 10 ? '0' : ''}${ month }-${ day < 10 ? '0' : '' }${day}`
}

var getDateArray = function(start, end) {

  return formatDate(new Date(
    start.getTime() + Math.random() * (end.getTime(0) - start.getTime(0))
  ));

}
var dateArr = getDateArray(startDate, endDate);


console.log(dateArr);

All I did here was add a call to your formatDate function within the getDateArray function so that now the return of the getDateArray will no longer contain timezone information.

Create these 2 functions to change the date format.

function DateFormat(startDate)
    {
        const strYear = date("Y",strtotime(strDate));
        const strMonth= date("n",strtotime(strDate));
        const strDay= date("j",strtotime(strDate));
        return "${strYear}$-${strMonth}-${strDay}";
    }

function DateFormat(endDate)
    {
        const strYear = date("Y",strtotime(strDate));
        const strMonth= date("n",strtotime(strDate));
        const strDay= date("j",strtotime(strDate));
        return "${strYear}$-${strMonth}-${strDay}";
    }