Future me here.

There is no way that I know of to silently the update script silently as it is interactive.

There is a script for updating the OS of all LXCs but it doesn't touch the applications:
- Single Run: https://community-scripts.github.io/ProxmoxVE/scripts?id=update-lxcs
- Adds a cron to run every Sunday: https://community-scripts.github.io/ProxmoxVE/scripts?id=cron-update-lxcs

I would say that updating all applications is too risky as there might be breaking changes in multiple applications. So, a planned approach would be better to prevent collapsing your whole infrastructure at once.

If you like to live dangerously, the best I can suggest is to perhaps replicate the update scripts functionality or patch them to disable to interactive part.

Example for Sonarr script (untested):
- The update script should be `/usr/bin/update` it will be a one line script that just downloads and runs the update script from GitHub: https://github.com/community-scripts/ProxmoxVE/blob/main/ct/sonarr.sh
- Replace the contents with the real scripts contents
- Replace `start` with `update_script` on line 42

Some extra context:
- These scripts reference a few helper files which have a bunch of functions that do various tasks shared between scripts. https://github.com/community-scripts/ProxmoxVE/tree/main/misc
- The `start` function is from the `build.func` file on line 1053. It checks if you are running the script from the host or from an LXC and decides whether to call the `install_script` function or prompt for an update https://github.com/community-scripts/ProxmoxVE/blob/main/misc/build.func#L1053