Offset

The Offset tool is used to duplicate and offset an edge loop at the intersection of boolean operators.
This way clean topology in the form of a perimeter loop is established in the periphery of the boolean operation.
It is not a general purpose offset tool.

Offset can deal with tricky geometry overlaps and significantly reduce manual cleanup work as a result of these overlaps.

Selection

Select a loop of edges or vertices. It should be a cyclic selection, otherwise non-manifold geometry will be created.

cyclic edge loop at boolean intersection or chamfer, a vert loop is fine as well

Using Offset

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