How to make the camera keep what it sees in a certain frame and continue to look at that frame in the next few seconds?

In addition, my scene has two cameras. How do I access the output texture of a specific camera in the code? The full-screen texture I want is not the render texture with a fixed resolution that can be created by right-clicking.

You probably need to expand on what you want to accomplish here for clarity.

Do you just want to add some stickiness to the currently looked position?

Do you want to save a snapshot of a frame then use that in some kind of special effect? (eg flash grenade)

Or do you want to something else that than?