To reduce storage usage on mirrors AlmaLinux 9.3 Beta repos are only available in Vault:
https://repo.almalinux.org/vault/9.3-beta/

For network install please use the following URL:
https://repo.almalinux.org/vault/9.3-beta/BaseOS/x86_64/kickstart/
(replace x86_64 with desired architecture: aarch64, ppc64le, s390x)

AlmaLinux Mirror Service and Anaconda installer redirect your AlmaLinux 9.3 Beta
system to Vault automatically.