Ad-blockers like uBlock Origin or AdBlock Plus have their own settings that override browser defaults. You may need to "Whitelist" the site within the extension itself.
Some Mac security software (like Norton, McAfee, or Avast) includes a "Web Shield" or browser security module. These act as a firewall for web traffic. how to unblock pop up windows on macbook
If you want to allow pop-ups on every website you visit (not recommended for security reasons, but useful for troubleshooting): Ad-blockers like uBlock Origin or AdBlock Plus have