I’m trying to render a 3D animation at the center of the screen, while keeping some other objects locked and fixed to a certain position on the screen, much like a HUD. I want to obtain something like this:

(credit to https://zerobone.net/blog/cs/linear-transformations-3d-manim/), where the matrix in the corner stays fixed, and the space rotates. I managed to do so by calling (eliding not relevant parts):

class MyScene(ThreeDScene):
    def construct(self):
        # [defining objects...]
        mobj_group = VGroup(mobj1, mobj2)
        self.play(mobj_group.animate.scale(0.3).to_corner(corner = UP + LEFT, buff = 0.3))
        self.add_fixed_in_frame_mobjects(mobj_group)

but this only works if you start by creating with the object you want to fix, then fixing it, and only then rotating the camera. If I want to add a fixed object at a later point in the animation, it moves relative to the scene coordinates, not the camera ones. For example:

See the two objects in the red rectangles (added after). The graph has been fixed with add_fixed_in_frame_mobjects BEFORE moving the camera, while the number was created and moved after. As a result, it has been moved relative to the scene axis, but how can I make it fixed in a corner of the screen, like the first graph? Thanks!