Hey there, thanks for raising this and providing such a clear summary (and for linking to the previous forum threads)! 
You’re absolutely right—this error:
E: Release file for http://deb.debian.org/debian-security/dists/bullseye-security/InRelease is expired (invalid since XXmin XXs). Updates for this repository will not be applied.
…is a recurring issue with the Debian security repository used by Streamlit Community Cloud’s build environment. When the “InRelease” file expires, apt-get fails for all apps needing system packages (like gdal-bin, qgis, python3-qgis), and rebooting or redeploying won’t help until the base image or apt sources are updated on Streamlit’s end. This is confirmed in multiple forum threads, including this one and this one, where the only resolution was a platform-side fix.
You’re not alone—others are likely affected, and the best course is to wait for Streamlit Cloud maintainers to refresh the build environment or apt sources. Deleting/redeploying or editing packages.txt won’t resolve it until then. Keep an eye on the Streamlit Community Cloud status page and the forums for updates.
Sources: