This thread discusses the case where you retain a BTRFS partition and overwrite one subvolume (typically /) while retaining others (typically /home). It refers to this as “Goal A”
This refers to the “old-style” Anaconda installer. I think the atomics are still using this, as is every flavour of Fedora except for F42 Workstation.
It doesn’t mention encryption explicitly, so I’m not sure whether LUKS complicates things.