Anchor points are open diamonds and circles (not solid)

I’m trying to figure out how to do diacritics and my anchor points are open diamonds and circles (not solid). What does that mean?
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Check pages 35 and 36 from Glyphs3 Handbook :

The red anchors are not the same as the anchors you might be referring to (nodes). Anchors in Glyphs refer to positioning references in the form of coordinates inserted into a layer. They do not show up as outlines.
Nodes are the things you draw.
Oncurve nodes: nodes on the outlines.
Offcurve nodes: what you might know as handles, the things to form the curves, which are between the oncurve nodes.