This is pretty chill. It's definitely something you can add on and flesh out.
The objective indicator got kinda broken when going form small to fullscreen, and i think i know why. In fullscreen, it was only drawing in a rectangle the size of the small screen version, and what i think you want to do is, when converting from your target's world position to the screen position, multiply the resulting x and y position values by the quotient of the indicator's parent canvas's rectTransform dimensions to the screen's dimensions. In addition, when you clamp the indicator's position to be on the screen, clamp it to the canvas's rectTransform dimensions.
I had the same issue doing my hud indicators, and that's how i solved it. Hope this helps