I can’t seem to find a way to use this anymore in the newer versions of Unity since the Image Effect packages are seemingly replaced by Post Processing Stack. Is it possible to have screen overlay for PPS?
You could pretty easily write a custom post processing effect that does this; get the template from the tutorial “Writing Custom Effects”:
https://docs.unity3d.com/Packages/com.unity.postprocessing@2.1/manual/Writing-Custom-Effects.html
Then you already have the current frame in the shader, all you need to do is to add another texture there and blend it somehow over the current frame. Instead of just using additive blending by summing up the values from two images, you could try implement some image processing app style blending mode. You can find many examples out there. Wikipedia is good starting point (Blend modes - Wikipedia).
You can check the PPS source codes for examples on how to implement the texture parameters and things you need.