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I think that your problem is that the default extrusion width in Prusa Slicer is by default 0.45 mm, slightly bigger than the nozzle diameter to give more quality and better layer adhesion, but since the modeled supports are thinner that the line width they are not being processed by de slicer.

To solve the problem you could either reduce the line width (Print settings->Advanced->extrusion width [Advanced]) or ask the slicer to process thin walls (Print settings->layer and perimeters->detect thin walls [Advanced]).