You can use RHEL as a repo server for AlmaLinux 8. What’s your actual issue?
From the looks of it, you may want to change:
baseurl=... to baseurl=https://repo.almalinux.org/almalinux/8.10/BaseOS/x86_64/os/
(or preferably a mirror), unless almalinux-binary is an actual server on your network.
If you reposync repos of multiple distros, then same -p /var/repo for each distro is probably not a good idea, assuming the distros have common names. (I have never used reposync, so don’t know what it puts under the “-p” location.)
The reposync is merely a wrapper that calls dnf with some options. Any distro that has sufficiently recent version of dnf should be able to download all YUM-repos.