If you are using 3D layers in After Effects, you don't even need a blur effect.
(Free version/presets): Sometimes bundled with hardware or available as specific free presets, Boris FX's version is highly regarded for its "Focus Target" features. 3. Legacy "Workaround" (Not Recommended) lens blur after effects missing free
This method is fully free but requires manual setup. If you are using 3D layers in After