On 17 October 2023 UBL 2.4 was approved as a Committee Specification:
https://docs.oasis-open.org/ubl/cs01-UBL-2.4/UBL-2.4.html
All resources can be downloaded from the main UBL 2.4 subdirectory:
https://docs.oasis-open.org/ubl/cs01-UBL-2.4/
And the complete CS in a ZIP file package can be downloaded here:
https://docs.oasis-open.org/ubl/cs01-UBL-2.4/UBL-2.4.zip