How to reproduce:
1. Create a new 2D URP project
2. Duplicate the “MainCamera“ and change its type to “Overlay“
3. Create a UI > Panel
4. Select the “MainCamera“ GameObject, then add the duplicated “MainCamera (1)“ to the Camera Stack
5. In the “MainCamera“ GameObject, enable “Post processing“ and change the “Anti-aliasing“ mode to “FXAA”
6. Observe the Game view

Alternatively:
1. Open the “CameraStackBug.zip“ project
2. Select “MainCamera“ and change the “Anti-aliasing” mode to “FXAA“
3. Observe the Game view

Expected result: The Panel is still rendered
Actual result: The Panel is not rendered

Reproducible in: 6000.0.51f1, 6000.0.52f1, 6000.1.9f1, 6000.2.0b7, 6000.3.0a1
Not reproducible in: 2022.3.63f1, 6000.0.50f1

Reproduced on: Windows 11 Pro (24H2), Ubuntu 24.04
Not reproduced on: No other environment tested

Notes:
- Only reproducible in a 2D URP project
- On Ubuntu 24.04, “Postprocessing Final Blit Pass/Draw UIToolkit/uGUI Overlay: Trying to load color backbuffer into a complex RenderPass setup, results undefined.” error is thrown
- The bug does not reproduce when the project is upgraded from the non-reproducible-in to a reproducible-in version. So it is recommended to repeat the first reproduction method for each version, to get the most consistent reproduction