Depends on your budget and electronic assy skills.
Most reliable has Tx on one side and Rx on the other side. at bumper height, which can share power with low current and 1 LiPo cell.
One method which has excellent immunity is like that used in TV remote controls with pulsed frequency bursts which are filtered to block;
• DC light (e.g. from tungsten bulbs sunlight)
• Continuous signals at any frequency
• Strongly or weakly modulated patterns from fluorescent lamps with electronic ballasts
A less reliable method can be made equality reliable by sinking the lens behind a matching 5mm D hole to attenuate any other light.
It can then be visible LED or invisible IR and pulsed for small duty cycle to reduce battery consumption on the Tx.
The Rx just needs to detect the pulse and stretch it with a diode & RC value and CMOS gate to act as a pulse stretcher and the LED indicator is ON.
When the pulses stop, by a blocked path the LED indicator turns OFF.
With this method the path by small 5mm tunnel can be made very precise or fairly loose and installer aimed by eyeball..
It can be made a sensitive to detect a 1mm object blocking the path or a finger size or bumper size merely by adjusting resistor values and hole depths.
IR Rx method
https://www.mouser.com/ProductDetail/Vishay-Semiconductors/TSOP32338SS1V/?qs=sGAEpiMZZMvAL21a/DhxMry5nKn3biWwC6ykjkKFOq0=
IR Tx uses a IR LED and a simple chip with passive parts to generate the clock burst and rep rate like a CD 4060.
THe problem with reflective sensors is the reflectance is ambiguity of detecting the car and amplitude. of stray reflectance, but possible to resolve.
edit...
It's not a problem to indicate the Red Grn LEDs as you requested. using a one shot cct.