I just started using it but I made a mistake on one of my submissions. Is there any way to undo or edit a submission made in the app?

Edit: There is an undo button on the bottom left in the app.

You've already received some great suggestions. Another one is Netdata. Personally, I use glances to collect the data and Home Assistant to display the dashboard. But I only do this because I already had Home Assistant running.

How are packages marked as insecure? I assume that's from some sort of automatic build process? Is that done in Hydra (https://hydra.nixos.org/)? Or is that from manual, or a lack of manual review?

I didn't find anything concrete, but it seems that a package is automatically marked insecure if it has a dependency that has a known CVE. I wonder how that is done.