It appears that the meta title tag cannot be changed for each blog post.
I have several blog posts that have long titles, where I need to change the meta titles to be shorter without changing the real blog title, as well as add some SEO to those.
See this idea: The ability to set a different H1 from <title> tag in blog posts is now in beta.
If you are interested in joining this beta and have not already reached out to me, please send me a message with your Hub ID and I will add you to the beta. Feedback is welcome!