Debian uses systemd as its default init system
Devuan was created specifically to avoid systemd, offering alternatives like SysV init, OpenRC, and runit
I do not know what an init system is. I don’t know what systemd is. I do not know what Devuan is. I do not know what SysV init is. I do not know what OpenRC is. I do not know what runit is.
I vaguely understand what debian is. Although I would be the wrong person it explain it. I know it’s the type of linux that ubuntu is. And I know it seems like every disto I look at says it’s based on ubuntu, and therefore is debian since ubuntu is based on debian.
What I don’t understand is if everyone hates ubuntu, but ubuntu is based on debian, but nobody hates debian, why is everything based on ubuntu and not debian?
How do I know if I want the debian version of a distro, or the devuan version? What are they even talking about?
I’m not an expert but have at least a basic enough understanding. I’m sure someone will come correct me /expand on plenty of things.
Think of systemd like a service manager. It’s software that orchestrates other software that is running. Like systemd will start to your ssh server service for you when the OS boots up, but it knows to wait until the main networking services are running first since ssh won’t work without networking anyway. That kind of thing. For systemd specifically, some people don’t like it because (and I may get this wrong) they don’t like one piece of software being so in control of how a system operates. They think it’s too overpowering, and prefer alternatives. I don’t understand enough about the alternatives and personally have only ever used systemd and it works perfectly fine for me.
As you say, Debian is a Linux distribution. People can fork (make a copy and edit it separately) Debian to make other distributions. This is what Ubuntu does. They’ll use Debian as a base, and make tweaks to it, and basically just made enough tweaks it was worth calling it something different. Other distributions like Mint take Ubuntu as their base and edit it into a whole new thing. Kind of makes Mint the grandchild of Debian in a way. The other main Linux base distros you’ll see are Arch and Fedora (there are others but they’re less common).
Devuan is just a fork of Debian (just like how Ubuntu is), but they decided to make their main edit be the removal of systemd, keeping most of the other things the same. (This is my first time hearing if Devuan, so there may be other significant changes I’m overlooking).
A lot of people don’t like Ubuntu because of the inclusions of specific systems. The one I see the most would be snap. It’s something that was made for end users to have things be easier, but it’s not the most efficient way to install programs so some people don’t like it.
As far as Debian vs Devuan, unless you have something against systemd, I would just stick with a Debian base since that’s one of the most common you’ll find, so there will be a lot more help available out there when you’re searching for things.
Hope that breaks it down well enough to get the basics of it at least!