I believe
Draw Sprites First is the command you are looking for though admittedly I don't think that works with 3D objects.
EDIT: If you're rendering all 3d to the cameras then putting the cameras into images for sprites that means there will actually be no 3D on the screen then you can just use Draw Sprites First
The best way would be to make what I call a Text Layer. A render target that you draw all your text to. Best thing about this is you only need to update it when you need to instead of constantly rendering text to it which we know text is the slowest thing on the planet. You could put it on a sprite with high priority so it sits on everything.
Another method would be to hide all sprites and just paste them. That way text will draw over.
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