Hey there, thanks for sharing all the details and welcome to the Streamlit community! 
The error you’re seeing—“Release file for http://deb.debian.org/debian-security/dists/bullseye-security/InRelease is expired”—means the apt repository for Debian Bullseye security updates is temporarily out of sync or expired, so apt-get can’t install chromium and chromium-driver from packages.txt. This is a known issue that sometimes resolves itself after the repository updates, but it’s not something you can fix directly in your code or config. Deleting packages.txt skips the apt step, which is why your app installs, but you lose the needed dependencies for Chromium.
This issue has occurred before and is usually resolved by waiting for the repository to refresh, or by deleting and redeploying the app after some time. If you need chromium and chromium-driver, you’ll have to keep packages.txt and try redeploying periodically until the repository is updated. For more info, see similar reports and solutions in the Streamlit forum and official docs on apt-get dependencies. If you’re still stuck, please share your repo and requirements so others can help debug!
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