I verified with 2 Tmo technical support reps and a Tmo engineer that the issue is provisioning on their end. Esims from other carriers may work with an unlocked device but the best we can get with Tmo is wifi calling for now. They expect fully support of esim when the stable version is released.
Some people with TMobile models have gotten it to work. Unlocked devices too with TMobile sims. Something is not configured properly software wise since some people with TMobile firmware are able to connect with a signal. Hopefully they'll figure it out.