Can you flour meat with SR Flour instead of plain for casserole?

No. SR flour should not be used to flour meat for casseroles.

Self-raising flour contains a raising agent, usually baking powder, which is activated when it comes into contact with moisture. When meat is floured with SR flour and then cooked in a casserole, the moisture from the meat and the cooking liquid will activate the raising agent, causing the flour to rise and become bubbly. This can result in an unappetizing texture in the casserole.