Welcome to the Shopify community!
and Thanks for your Good question.
It can be done by doing some code customization. Please take the help of a developer and hire Shopify Expert or me
Eunice here from the Shopify team. Thanks for your post!
To create a pop up for any of the Shopify free themes, Brooklyn included, you'll need to use a third-party app from The Shopify App Store. There a few apps available which you can view here, but I'll list my top three recommendations below:
1. Privy ‑ Pop Ups, Email, & SMS - This is one of the more popular pop-up apps, and you can easily see with its 24405 reviews!
2. Pop Up, Email & Exit Pop Ups by Poptin - My personal favourite. It's so easy to use.
3. Original Wheelio spin pop‑ups by IT Trading d.o.o. - if you're looking for something a bit different, this is it! It does cost to use though, from $14.92 USD per month.
I hope this helps! Are you looking to get a pop-up created ahead of Black Friday Cyber Monday? Great plan if you are! It's super close now, but if you have time, I urge you to view this great blog. It's the 27-point checklist to prepare your store for Black Friday Cyber Monday.