Question Need help with lingering light trail

I've been stuck on this part of my project all week and I'm not too sure how to continue.

The goal for this mechanic is to basically be a flashlight. I want to have the player be able to click in a direction and an invisible projectile bounces across objects, Pong-style, leaving a lingering light trail where the back of the trail slowly fades away while the object continues to bounce around, keeping the trail at a fixed length. I've tried using 2D lights and experimenting with shader graphs, but everything I've tried so far has failed and I'm not sure how to proceed and need some help.

Does anyone know how I should start implementing this?