Hi @arek It's way too easy what you have to do is to put the following code to Settings > Advance > Code Injection>Header ,What this code will do it will pop up every time user visit the website.
<script>
window.localStorage.setItem('test', '0');
window.localStorage.setItem('squarespace-popup-overlay', '0');
</script>
Tested and it worked perfectly fine , Hope it works perfectly fine for you 🙂
NOTE: TEST IT ON INCOGNITO OR ON PRIVATE WINDOW.
If it works for you don't forget to mark it as solved by clicking arrow on top left of this answer 🙂