Often when marking things up I have a difficult time when background images and prior markups keep getting accidentally selected or moved when placing new markups on top.
Please add an option to not select locked markups. So when this option is active and a markup is locked, it will not be selectable by 1) mouse click, 2) lasso selection, 3) CTRL+A. Locked markups would still be selectable using the markups list.
This option could go under Preferences > Tools > Markup. It would be helpful to have a toggle for this option on the status bar.
Alternatively, allow the Layer > Lock option to have this behavior. So if you put markups on a layer and lock that layer, it would make all the things in that layer not selectable other than through the markups list.