I have reported the issue and it’s being tracked, but I don’t have an ETA on when it will be addressed for sure. I was able to further refine my understanding though: this bug is triggered if your requirements file results in streamlit <=1.19. So you should be able to pin as far back as 1.20 without triggering the bug.
What happens when Community Cloud detects Streamlit is version 1.19 or lower is that altair<5 gets installed afterwards, all by itself. So it’s altair’s dependencies in particular that get upgraded, even if altair was already pinned and installed at a compatible version. This is a workaround because altair wasn’t pinned in Streamlit’s dependencies at the time. I’m watching the ticket for when they patch the workaround. The hope is that (once patched) users will be able to avoid the error by pinning the correct version of altair themselves. I will definitely post an update when I get confirmation that it’s fixed or have a definitive schedule.