The oldest Linux distro that's still maintained to this day.
With an extreme focus on the KISS principle (simplicity in design) and stability.
It basically still works the same way it did 30 years ago.

The linux distro you want to have on a usb stick if the apocalypse breaks out.

One of the original Linux distributions. It was created in like 93 or 94.

With Slackware, you install its entire repository (~15GB) upfront. This gives you a system with a lot of software pre-installed for a wide variety of tasks, and makes dependency resolution for the base system pointless - all dependencies are already installed.

Additional software is installed via Slackbuilds or community-maintained additional repos. Those work very similar to Arch's AUR: officially you are supposed to download, build and install packages manually using preconfigured build scripts with no dependency resolution, but tools that automate the entire process are available. And just like with the AUR, those tools aren't officially recommended, but they work and almost everyone uses them.

So while it's true that the default package manager in Slackware has no dependency resolution, that's irrelevant in practice.

One word of warning: While Slackware does work well out of the box, adjusting it to your needs is a more involved process than with other distros. Everything is done manually but it lacks the awesome documentation Arch has and includes some pitfalls due to lack of automation we're used to nowadays. For example, if you upgrade your kernel and reboot, it won't boot. Because you forgot to copy the new kernel into your EFI partition, regenerate the initramfs and point your bootloader to it. Every other distro's package manager recognizes a kernel upgrade and triggers those things automatically.

Slackware is easiest if you are a bit flexible in what you use and are fine with its default selection. If you want Gnome, best choose another distro. It's possible to build and set up, but not easily.
But once you've set everything up the way you like, it just stays that way forever and there is almost no work needed to maintain it.