Choose Format - Arrange - Send to Back (LibreOffice Writer, LibreOffice Calc).
Choose Shape - Arrange - Send to Back (LibreOffice Draw).
Shift+āĻāĻŽāĻžāύā§āĻĄCtrl+āĻŦāĻŋāϝāĻŧā§āĻ āĻāĻŋāĻšā§āύ (LibreOffice āĻāĻŽāĻĒā§āϰā§āϏ, LibreOffice āĻĄā§āϰ)
Open context menu - choose Arrange - Send to Back (LibreOffice Impress).
āĻĒāĻŋāĻāύ⧠āĻĒā§āϰā§āϰāĻŖ