Yum was used on way more than Yellow Dog Linux. CentOS, Fedora, RHEL, etc all did

Yes, it's a command from apt-get that apt only passes through:

--auto-remove, --autoremove
If the command is either install or remove, then this option acts like running the autoremove command, removing unused dependency packages. Configuration Item: APT::Get::AutomaticRemove.

--with-new-pkgs
Allow installing new packages when used in conjunction with upgrade. This is useful if the update of an installed package requires new dependencies to be installed. Instead of holding the package back upgrade will upgrade the package and install the new dependencies. Note that upgrade with this option will never remove packages, only allow adding new ones. Configuration Item: APT::Get::Upgrade-Allow-New.

-U, --update
Run the update command before the specified command. This is supported for commands installing, removing, or upgrading packages such as install, remove, safe-upgrade, full-upgrade. This can be useful to ensure a command always installs the latest versions, or, in combination with the --snapshot option to make sure the snapshot is present when install is being run.

https://manpages.debian.org/trixie/apt/apt-get.8.en.html

Snaps I agree just because there is no open source snap store and it’s impossible to set up a 3rd party store.

Flatpaks though? They let people install packages with weird / rare / not available requirements on any distro. All open source with a really nice sandbox. I think flatpaks are great.

Let's look at the alternatives:

• System packages: not viable for the majority of packages because the distro devs don't have time to manually package everything
• AppImage: even worse integration (like no desktop shortcuts on install). Developer has to guess what libraries need to be included and which ones are already installed by the user. No sandboxing. Probably worse SLSA scores.
• AUR: even worse security. No sandboxing. Packages are often compromised by hackers.

Immutable Linux users didn't like that

There's apt-cache search, but I just prefer doing it with the package manager tbh :p