1mm height SMD LED can be placed upside down.

https://www.electronics-lab.com/1mm-height-smd-led-can-placed-upside/

Kingbright KPTR series, suitable for reverse mounting, makes it possible to achieve that the LED is hidden in the PCB. Naturally, manufacturing LED with a zero height is most likely unreal at the current physics status and 3D experience of the world. Nevertheless, it´s still possible to reach the goal that the LED wouldn’t stick […]