The transition from "Lens Blur" to "Camera Lens Blur" changed the internal "match names" of the plugin, meaning After Effects no longer recognizes the old effect as being the same as the new one.
You downloaded a free Lens Blur plugin, installed it, restarted After Effects, and... nothing. It is missing from the effects menu. lens blur after effects missing free
This is the direct replacement for the old "Lens Blur." It is faster, offers better edge handling, and is built natively into After Effects (no plugin required). The transition from "Lens Blur" to "Camera Lens