PSA: LineageOS 17.1 is no longer getting official builds, even though it has some of the recent security updates committed. So if can't upgrade immediately to 18.1, you can do a build yourselves to get the security patches.
I just wish the devs clarified timelines around merges (but not builds) on older branches.
"When it's ready."
Stuff is merged in once it's well tested and ready. It also is only updated as long as someone still cares to update it.