You can match instead of using split.

function pntSq(m){
  return m.match(/[A-Z]{2}/g);
}

console.log(pntSq('YYRR'));

Link: regex101

This matches any 2 uppercase letters together, but note that they may be different.

[A-Z]{2}

To match the same uppercase letter 2 times. This ensures that it's the same letter repeated and not different letters.

([A-Z])\1

JavaScript may not support splitting on lookbehinds. One workaround would be to do this in two steps. First we can replace on the following regex pattern:

([A-Z])(?!\1)(?=.)

This will capture any capital which in turn is followed by a different letter (and also not the end of the string). Then, we replace with a single space. As the second step, we simply split on space to get the output array we want.

function pntSq(m) {
    m = m.replace(/([A-Z])(?!\1)(?=.)/g, "$1 ");
    console.log(m);
    var a = m.split(/ /g);
    console.log(a);
}

pntSq("YYRRAAABBBBBCC");