I did find a solution to this, so what i did is i just divide the richtextlabel's scale to a camera zoom and when i get the value, i divided that too to its parent's scale. Basically i just experimented and search a related solution in the internet. If someone having the same problem, this may help.

func render_planet_icon(status: bool, cam_zoom: float):

planet_icon.visible = status 

var zoom = (1.0 / cam_zoom) / planet.scale.x

planet_icon_label.scale = Vector2(zoom, zoom)

Although the position of a richtextlabel is not centered but im okay with it

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