Hi Hilary and David,I've been similarly frustrated, although I had a meeting with the Flex Product Manager who assured me GTM integration would be possible in H1. As it's a one page application, it's not currently possible to add the code to both the header and footer. I've had some success with adding the header code (without script) which is allowing us to fire tags.
From an SEO perspective, I'm also having difficulties. If anything Flex is a step back on the capability you had with Classic.
I want to circle back on this thread to let everyone know that we elevated your concerns to the product and support teams.
The product team is looking into approaches to make using Google Tag Manager (GTM) in Cvent easier but are still in the research phase so they cannot provide an expected timeline. To follow the status of GTM enhancements I encourage you to upvote and follow the Google Tag Manager (GTM) vs Google Analytics (GA) idea in the Ideas section of the Community.
In the meantime, the support team is also looking if there is further guidance or additional documentation or that can be added to the Knowledge Base.Thank you all for your candid feedback!