TdyFq‖Choose Format - Arrange - Send to Back (LibreOfficeDev Writer, LibreOfficeDev Calc).
5pzCr‖Choose Shape - Arrange - Send to Back (LibreOfficeDev Draw).
cG5R9‖Shift+CommandCtrl+minus sign (LibreOfficeDev Impress, LibreOfficeDev Draw)
NkXED‖Open context menu - choose Arrange - Send to Back (LibreOfficeDev Impress).
A873M‖