Hey there, thanks for sharing all those details and for your thorough troubleshooting! 
This “infinite loading spinner” with logs stopping at “Spinning up manager process…”—before any repository cloning or dependency installation—almost always points to a backend or orchestration issue on Streamlit Community Cloud, not a problem with your code, repo, or config. Multiple users have reported this exact symptom, and it’s often resolved only by a platform-side fix or service restart. Your steps (reboot, Python version change, code validation, Codespaces test) are all the recommended actions, so you’ve covered the bases.
If the logs never reach the repository cloning step, it’s not an app or requirements issue. The best course is to monitor the Streamlit status page and forums for outage updates, and consider submitting a support request if you haven’t already. For more info and similar cases, see the official docs and forum threads: App stuck at spinning up manager process, App deployment stuck after processed dependencies, and App loads indefinitely. Community members, feel free to jump in if you’ve seen a recent workaround!
Sources: