In December 2017, Google told us to avoid using Google Tag Manager for SEO experiments or SEO solutions. In fact, it was not supported with Google's testing tools but now Google may have changed their minds...
A new article from SEMRush named How to Add FAQ Schema to Any Page Using Google Tag Manager goes through the steps on how to add FAQ schema to your pages using Google Tag Manager. When Cindy Krum asked Google's John Mueller about this on Twitter, John said "Reading the linked article, it seems quite complete and balanced - I think it's fine." He even added "Happy to see more sites trying out new structured data types!"
Here are those tweets:
Reading the linked article, it seems quite complete and balanced - I think it's fine. It also touches on the aspect you mentioned, using GTM vs on-page markup. Happy to see more sites trying out new structured data types!
— 🍌 John 🍌 (@JohnMu) June 13, 2019
I guess as time goes on, people can change their minds. If anything, this shows - test, test, test and don't just listen to advice from Google or posts here that give you advice from Google. :)
Forum discussion at Twitter.
