Reproduction steps:
1. Open the attached “BugRepro” project
2. Open the “Assets/Scenes/Main” scene
3. Enter Play mode
4. Press the “K” button
5. In the Hierarchy window, observe the “Entrance Room” GameObject

Expected result: A new “Viewport“ GameObject was created as an “Entrance Room” GameObject child
Actual result: No new GameObject was created

Reproducible with: 1.6.1 (2022.3.5f1, 2023.2.0b1), 1.7.0, 1.8.0-pre.2 (2022.3.14f1, 2023.2.3f1, 2023.3.0a17)
Couldn't test with: 2021.3.33f1 (compilation errors while importing the project to this version)

Reproducible on: Windows 11
Not reproducible on: No other environment tested