I feel like there’d be a way to do this using postprocess materials. Just use SceneDepth to get the depth value of the pixel; it’s not a 1:1 correlation with the Time value of the trace but it DOES report absolute distance of the pixel from the screen. You can use the depth value to color the pixel and discard/blacken any pixels too far away.
The tricky part (at least for me) would be discarding and merging pixels to reduce the resolution from 1:1 pixel mapping to something low-res. It’d probably be possible with the Screen Size setting in a post-process volume; simply Set that to 25, apply the postprocess material that maps depth to color, and you’d be very close.