As far as Linux distros are concerned, really, any distro is just a package manager with repos and a set of default utilities. Essentially, a distro is an opinion on how you should use your system, not a law. Now prepare for my ADHD-fuelled stream of consciousness (which I wrote instead of getting any work done, yay):

Stay away from Arch and Gentoo for your first distro. These are basically meme distros, especially Gentoo. They allow for a lot of flexibility and building a really minimal install, but come with install-time complexity you really don't need. Try them later on if you're interested. Stay away from nixOS for now too, although it's also awesome.

Package managers

Essentially, you have two main packaging types: RPM (used by Fedora/RedHat's dnf, previously yum and (Open)SuSE's zypper) and deb (used by apt mostly, dunno if others).

Either one is fine, but I think you'll probably find more software available as debs. But the difference barely exists and with GUI apps you can usually install a flatpak anyway (more on this later).

Deb

Everything deb/apt comes from the Debian lineage.

You have Debian, the granddaddy of stability, releases come every few years and are tested thoroughly. After package freeze, only bugfixes and security updates usually get added. Then you have Ubuntu, a fork of Debian with more frequent releases as well as Long-Term Support releases every 2 years. Ubuntu used to be the most recommended beginner distro, but it's no longer the case - not just because it has ads in it, but also because it pushes Snaps over Flatpaks AND occasionally tries to force Snaps over regular packages (again, more on this later).

Then, much like Ubuntu has forked Debian, others have forked Ubuntu. There's Linux Mint - used to have the same release cadence as Ubuntu, but now they only base their releases off Ubuntu LTS versions. Really, it's Ubuntu without all the commercial stuff Ubuntu's been pushing. And they maintain their own desktop environment(s), but you can get those elsewhere too. There's also Pop!_OS which is developed by System76, a laptop manufacturer. It used to come with its' own customizations on top of Gnome, but now they're creating their own desktop environment altogether, which is currently in Alpha 2. And then there's KDE Neon, which is also based on Ubuntu LTS, but it ships the latest version of KDE Plasma desktop environment, rather than whatever version is in the latest Ubuntu LTS.

Rpm

On the rpm side, you mostly have two families for non-enterprise users: Fedora, which has a similar release cadence to Ubuntu, but apparently keeps packages more up to date between releases and OpenSuSE, which has Leap (new versions every year, with critical bugfixes and security updates in the meantime) and Tumbleweed, which is rolling release, so you just get the latest version of every package that has been tested, rather than having to wait for a new release. Tumbleweed gets updated just about every day. There's also Slowroll, which gets big updates monthly, but can still get bugfixes between those.

Desktop Environments

For just about any distro, you can get just about any desktop environment. Ubuntu and Fedora default to Gnome. KDE Neon is pretty much just meant to be used with KDE Plasma. Pop!_OS defaults to customized Gnome unless you get the alpha version of the new COSMIC desktop. OpenSUSE defaults to KDE Plasma.

For Ubuntu you get variants like Kubuntu, Xubuntu, Lubuntu, etc, for whatever desktop you want, or you can switch alter (apt install kubuntu-desktop for an example). For Fedora, you can get a Fedora Spin, like Fedora KDE Spin for an example. Or you can similarly switch: dnf install @kde-desktop-environment. Same goes for all of them, really.

Desktop environments: The two big ones are KDE Plasma (close to Windows in default appearance, but a lot more customizable, and more functional straight out of the box) and Gnome, which as of Gnome 3 is just... unique, I guess. It's different. Then on the "Help I'm running this on a computer from 2004" side you have things like XFCE and LXQT. (Xubuntu, Lubuntu get their names from these). Those work just fine too, just a bit less eye candy. There are a lot more of less mainstream ones like Budgie or Enlightenment, but you can worry about those later.

Sandboxed applications - Flatpak, Snap

Now, why did I mention Flatpaks and Snaps earlier? Those are sandboxed package managers. A package comes with a sandbox of its' own, and Flatpak or Snap keeps a copy of all the libraries it depends on, instead of using system libraries. This means that 1) There's never a version conflict between what's installed on your system and what the application uses and 2) You have multiple copies of some libraries (Flatpak and Snap both I think do try to deduplicate though so if two applications use the same version of a dependency, it keeps one copy stored). 3) You can install applications your distro doesn't even have a package for.

Both also keep system resources out of reach of the applications, so they're more secure to some degree if you don't trust an application. This comes with limitations, too - sometimes you NEED your application to have access to something that's limited in Flatpak or Snap. You can sorta fix this with flatseal for Flatpak, but it's not perfect.

The real problem with Snap, besides having a proprietary backend vs Flatpak where you can use either Flathub or another application store with it, is that Ubuntu is starting to force it upon you - including for applications you may not want to run in a sandbox at all. You'll run apt install firefox and it'll play a trick on you and install the Snap instead of the deb. You lose some control over your system and how you use it. You can override this, but it's possibly more work than you'd want to take on as a brand new Linux user.

At the end of the day, I recommend using either OpenSuSE Tumbleweed (if you want latest and greatest always), Fedora, Linux Mint, or Pop!_OS. If you really want the latest and greatest KDE Plasma and don't want Tumbleweed, then KDE Neon might make sense for you.