Ubuntu ‘Noble Numbat’ 24.04 LTS beta is delayed due to the xz/liblzma security update causing a rebuild of binary packages.
Beta release is now due 11th April 2024 from the previously scheduled 4th April 2024 release date.
Ref: https://discourse.ubuntu.com/t/noble-numbat-beta-delayed-xz-liblzma-security-update/43827