I drew a raw oval and converted it to curves. When I use Optimize Selected Shape, I see nodes reduced. However, when I close the dialog box, the node count reverts back to the original count. I couldn’t find any info in the docs.
The blue squares along your oval’s curve are not nodes, but handles for your nodes- moving them will adjust the curve between the node they’re connected to and adjacent nodes. They show when you select a shape with the ‘Edit Nodes’ tool enabled, but do not show when you have the ‘Optimize Shapes’ window open and a given shape selected. So their reappearance does not in itself mean your changes are not being applied.
However, I can also see from your ‘Optimize Shapes’ window that you have not adjusted the amount of nodes in your oval- at the bottom it says ‘38 points -=> 38 points’- so there are no changes to apply. Try enabling ‘Smooth source shapes’ and adjusting that slider as well as the ‘Fit shapes to arcs’ slider.