I'm trying to make a html element with a preselected value but it seems to be random if the value I want to be preselected is the one selected or not

// elementName is a string and trueOrFalse is a boolean
let n = document.createElement("select");
n.id = elementName;
let opt1 = document.createElement("option");
opt1.value = true;
opt1.innerHTML = true;
let opt2 = document.createElement("option");
opt2.value = false;
opt2.innerHTML = false;
n.appendChild(opt1);
n.appendChild(opt2);
Form.appendChild(n);
let element = Form.querySelector(`#${elementName}`);
element.value = trueOrFalse;

Other ways I have used to try preselecting the value of the element n are :

if (trueOrFalse) opt1.selected = selected;
else opt2.selected = selected;
//and 
n.value = trueOrFalse;