Create jsx file?

(function moveOnProximity() {
var comp = app.project.activeItem;
if (!comp || !(comp instanceof CompItem)) {
alert("Please select a composition.");
return;
}

var layers = comp.selectedLayers;
if (layers.length < 2) {
alert("Select at least two layers (one leader and others to be affected).");
return;
}

var leader = layers[0]; // The first selected layer is the leader
var others = layers.slice(1);

app.beginUndoGroup("Proximity Movement");

for (var i = 0; i < others.length; i++) {
var layer = others[i];

// Add expression to the position property
var expr = `
leader = thisComp.layer("${leader.name}");
leaderPos = leader.position;
myPos = position;
threshold = 150; // Distance at which movement happens
force = 50; // How much the object moves

dist = length(leaderPos, myPos);
if (dist < threshold) {
moveDir = normalize(myPos - leaderPos);
myPos + moveDir * force * (1 - dist / threshold);
} else {
myPos;
}
`;

layer.property("Position").expression = expr;
}

app.endUndoGroup();
})();

<>
// Get the active composition var comp = app.project.activeItem; // Check if a
composition is open if(comp != null &amp;&amp; comp instanceof CompItem){"{"}
// Check if the square layer exists var squareLayer = comp.layer("Square");
if(squareLayer != null &amp;&amp; squareLayer instanceof AVLayer &amp;&amp;
squareLayer.source instanceof SolidSource){"{"}
// Set keyframes for scale and color over 15 frames var duration = 15; var
endTime = squareLayer.startTime + duration; // Set keyframes for scale
squareLayer.property("Scale").setValuesAtTimes([squareLayer.startTime,
endTime], [[100, 100], [0, 0]]); // Set keyframes for color
squareLayer.property("ADBE Color
Control-0001").setValuesAtTimes([squareLayer.startTime, endTime], [[1, 1, 1],
[1, 1, 0]]);
{"}"} else {"{"}
alert("Square layer not found or is not a solid layer.");
{"}"}
{"}"} else {"{"}
alert("No active composition found.");
{"}"}
</>

Copy an existing .jsx file from the folder Apps/Adobe Illustrator 2021/Scripting, replace the content with the suggested code and save it. After that, I was able to load the script into Illustrator. 

When I created a totally new jsx file, I also got the error message (syntax error)