Users error: Scene contains two "Base" cameras with "Unintialized" background and the cameras priorities are reversed "Second camera" has priority -1, so it gets rendered first, and the "First camera" has priority 0, so it gets rendered last, "Base" cameras are not suppose to combine their output, and the "Uninitialized" background is undefined and vary by platform.
To properly combine multiple cameras rendering there has to be one "base" and others "overlay" cameras: https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@15.0/manual/cameras-advanced.html