I’ve been using a lot of Debian based distributions recently after half a year on Arch. The main thing I miss a lot is the AUR. The convenience of having all my packaged in one format is a huge reason why I use Arch. Is there anything like it for the AUR?
I also think that things like Flatpaks and Snaps could be useful, as I don’t really want to have tons of repositories for tons of programs I install.
AUR like stuff is simply not for Debian. You are expected to only use software in the official repos.
If you want AUR you should really use Arch Linux or a easier alternative like EndeavourOS.
If you really want AUR (like thing) on Debian I recommend the nix package manager. It will do it’s own thing without messing with the host OS.