AggPoly (aggregate polygons) is a QGIS3-Plugin for aggregation and generalization of polygons within a certain distance with respect to barriers. The algorithm takes a polygon and optional barrier layer (of any geometry type) and returns features that link areas, which are within the specified distance. If a barrier layer is chosen, the new features don't cross the features of the barrier layer.
The algorithm relies on polygon vertices. Consequently, complex input polygons with a high vertex count have a huge performance impact! If possible and without substantial downside, simplify / generalise your input.
A lot! This is still a prove-of-concept!