This problem has cropped up several times in the past and drove me crazy because the fix was rebuilding stuff but I never learned what was going on,
To recap, when looking through the camera in the viewport, everything is blank, not even an outline of the camera. Limits and scaling were not the problem. Even adding a new camera would have the same problem.
Today I figured out it’s a bug in the viewport itself. Here is a really simple fix, I really hope it helps others:
-You need to destroy the viewport window. In my case I merged it with the Timeline window below it so the whole combined window is a Timeline.
-Then I split it again so I ended up with two Timeline windows.
-Change the newly made window back the Viewport mode, camera works again!
I’ve seen similar posts about the same issue but the one fix I tried did not work but it got me thinking about the Viewport when I realized the camera view was working in other Workspace tabs.