For images, you can use a photo library application like digikam and set tags on the files, which are saved both to a relational database and to the photo metadata inside the image file. For other file types I don't think there's anything standard.
I think it might store tags in linux file system xattrs so other software (or scripts) could access and index it.
I guess it switched desktop environments on you? If you're logged out there's supposed to be a way you can switch between desktop environments. It makes sense that the GNOME Settings app would only change wallpaper settings for GNOME, which I think is the main Ubuntu desktop environment. Are you sure you didn't upgrade to a version of Ubuntu that uses XFCE instead of GNOME?
The S3 "sleep state" of the computer. Which I guess is sleep. There sre other numbers for running and off I think.
They did this same thing with Mocrosoft Teams. Microsoft execs are some of the dumbest laziest people.
tmux has long been the better replacement to screen. SFTP makes it so you can use desktop software for file system operations.
I don't know how helpful it is to split stuff out like that. Especially grouping so many things under "default applications and daemons", which is most of what a desktop distro is. Also depends largely on a PC vs server setup.
should list an init system as its own bullet, which others have mentioned.
"one or more shells" doesn't mean that much. Yes, every distro includes one but the only difference between a terminal and any other application is that a terminal needs to be able to escalate to root privileges. You can think of it as just another default (but special) application. A lot of stuff that people think about when they think of Linux distros is just various clever mechanisms for supporting the terminal shell. Like the PATH environment variable. If you are using actual desktop applications other than a terminal, there isn't any interaction with the terminal shell application.
There's also fwupd, for updating firmware (your hardware is gonna be running out of date/buggy/insecure code if you don't have this).
The dbus daemon falls under the "daemons" bullet but it's pretty important, like wayland/x11 it's another IPC mechanism you need for programs to work correctly.
There's also the sound system. PipeWire is the modern one that implements the interfaces of various other sound systems so existing applications work with it. https://pipewire.org/ (PipeWire also has its own IPC protocol like dbus/wayland/x11).
flatpak, snap, distrobox, toolbox, docker, podman, etc. for running sandboxed PC/server applications. I assume there are some programs that are flatpak-only these days.
gsettings/dconf for Windows-registry like config that many programs use.
There's also plugging in an implementation of the glibc Name Service Switch, which allows libc to use a mechanism other than /etc/passwd and related files for user accounts, internet service names, DNS resolution, etc. . systemd can provide NSS implementations using its own user account mechanism.
Maybe there's just wasn't any data written past the partition point yet?
"because everyone else will be classified an independent contractor" 
Unity is GNOME, but it's the official name of Ubuntu's customized GNOME.
Maybe also add a criteria that they depend on X11, Wayland, (will still include libraries like java) or GUI toolkits like Qt or libadwaita/gtk.
Tor and Tails merge to support western intelligence