-r--r--r-- au
-rwxrwx--- au
You can use au 📲 to backup you installation files in Termux, i.e. debs. If you find your system unstable after updating, you can try to use dpkg --purge pkg_name and then dpkg --install pkg_name from /sdcard/debs to downgrade packages to a previous version of a package in the hope of regaining system stability in Termux.
You should use au from your $PATH. To see your $PATH, type $PATH +enter/return. Then use mv au destination_directory to move au to your $PATH. au +enter/return will update and backup your Termux Packages in three keystrokes!
Every time you want to apt update && apt upgrade or pkg up, you will also be backing up your former installation debs to /storage/emulated/0/Android/data/com.termux/txdebs by using au. Ideally, you should change /storage/emulated/0/Android/data/com.termux/txdebs to an external mirco SD card destination in lines 8 and 10 of au to save space on device.
If you find your system unstable, you can use dpkg --purge pkg_name and then dpkg --install pkg_name from /storage/emulated/0/Android/data/com.termux/txdebs to downgrade packages to a previous version of a package in the hope of regaining package stability.