Once I installed the beta and downloaded rtx supported worlds all I could see was pitch black and occasionally light shining through places but as soon as I turned rtx off the world was normal. My system is all basically brand new and I have a nvidia GeForce rtx 2070 super with 32gb of ram and an i7 9700k. I see no obvious issues as to why the beta wouldn't be working.
Linked issues
Comments

You will need to update your drivers. See MCPE-69401.