Hi,
Sorry for the late reply. Thanks for the suggestion!
I’ve checked and PopUp Builder is version 3.71
Then I thought maybe it clashes with some of the plugins after upgrading WordPress (it worked fine before upgrading WordPress to 5.6) So I disabled other plugins one by one and found out that after disabling plugin called “Disable Gutenberg”, the Popup Builder plugin worked.
I think it’s a clash between plugins that causing it, not sure but it works now and I’m happy ??
I can live with the new Gutenberg editor, hate its interface but not a big deal.
Regards,