You can use this code to Code Injection Footer (or Page Header Injection) to make Gallery Reel autoscroll in Squarespace.
<script>
(function docReady(fn) {
// see if DOM is already available
if (document.readyState === "complete" || document.readyState === "interactive") {
// call on next available tick
setTimeout(fn, 1);
} else {
document.addEventListener("DOMContentLoaded", fn);
}
})(() => {
if (window.location == window.parent.location) {
const reelControls = document.querySelectorAll('.gallery-reel-control [aria-label="Next Slide"]');
reelControls.forEach(reelControl => {
(function reelTimer() {
setTimeout(() => {
reelControl.click();
reelTimer();
}, 2000); // change this value to change the speed
})();
})
}
});
</script>