When I started using LineageOS on my Redmi Note 9 Pro, there were a couple of releases available, one was LOS 18.1 and the other one was LOS 19.1, but as time went, the los 18.1 downloads were gone and then the same happened to the 19.1 releases.
Thankfully, I have the version that I want already downloaded in my machine, but if someone wanted to download now those prior versions… well, good luck it seems.
Edit: yes, I know about archive.org, but can’t download.lineageos.org provide access to prior versions somehow? Is it because of storage costs?
As of March Android 11, meaning LineageOS 18.1, is no longer getting security patches. They probably don’t want to advertise that version. I don’t know about 19.1.