• Use a single global MouseArea and turn delegate into an Item
• Use a single Rectangle for both "today" and "highlighted" state
• Add font.pointSize: -1 workaround in the other labels to avoid runtime warnings

• Hovering and selecting items still works, updates agenda as needed, also "has appointment" overlay still works
• Switching between months updates the highlight - you can see a brief transition from gray to blue and then invisible when you move between the current month and others as the single Rectangle will transition from gray to blue in response to becoming "not today" and opacity 1 to 0 in response to being no longer selected, not too terrible, though.
• Pinch to zoom still works
• didn't notice stray highlight when closing popup with mouse still hovering

Unfortunately did not result in a noticeable speedup of first invocation