This Magento 2 extension displays popup with promo text and coupon code.
The promo text comes from custom block and coupon code should be copied from active cart price rule.
The popup can be displayed immediately or after x seconds.
Pull in the extension through Composer:
composer require "mikielis/magento2-module-popup-promo:*"
OR
download zipped extension and add its files to [magento root directory]/app/code/Mikielis/PopupPromo directory and follow listed steps from the official guide: https://devdocs.magento.com/guides/v2.3/comp-mgr/install-extensions.html