With this node setup you can smooth merge your instances with the main object.
The normals of one object are blended together to create an optical fillet edge that you can scale with parameters.
The nodes can be used with instances or with singular objects as well.
This method keeps the speed in your geonodes because it is much lighter than creating actual filleting geometry.

VERSION 4.5
June 20, 2025
Auto mesh island smooth normals
Automatically calculates all fillets of separate mesh islands

VERSION 4.5
June 6, 2025
New setup using new "set mesh normal" node
Simpeler and more versatile node setup
Compatible with belnder 4.5

VERSION 4.4
June 5, 2025
Release