It seems to me from testing that T-Mobile's 464XLAT implementation has recently been changed to block UDP. To bypass the problem if you change your phone/hotspot's APN (Access Point Name) to use IPv4/IPv6 instad of just IPv6, then UDP starts working on 5G (and LTE).
Already have an account? Login
Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.
Sorry, we're still checking this file's contents to make sure it's safe to download. Please try again in a few minutes.
Sorry, our virus scanner detected that this file isn't safe to download.