a critical error on my website

I have a critical error on my website in the tag page and default search results page. Please help me to fix the issue.
As I realize the theme that you are showing as a demo and the theme I have downloaded are not the same. There are some differences in the UI.

My tags page
vs
Your tag page is different.
My question, answer and comment submission interface is different than Yours.

I think your themes are backdated, there still an option for adding Google+ link as a social media.

Google+ shout down in april 2019, more than three years ago.
Why things should be like this? Please update the theme and plugin and help me to fix the issue.