I’ve had this issue for a while, but I’ve not spotted it mentioned by anyone else, so maybe this is not a bug, but my Mac.
Each time I open Rhino, the Left Sidebar has four and a half columns of icons showing, by increasing the width of the Sidebar and then decreasing it back to its minimum width, the Sidebar will correctly show four columns. This action will need to be done again when a tool that has an edit boxe is selected, as these are often also wider than the Sidebar.
I’m not sure if this started after the most recent release of Rhino, or after one of the last Apple OS updates.
Sorry if this has been mentioned before, I’ve searched the forums several times, but not spotted anything.