Linux

1). It matters a little bit, but not a ton. A big difference will come down to what package manager comes with a distro, and whether it is a "rolling" distro that gets updates as soon as they come out, or one which withholds updates until after they have some time for bug testing, etc. Given that gaming is one of your primary use cases, I would recommend a rolling distro. If your distro does not come prepackaged with something you can usually install it. Minimalist distros like Arch come with almost nothing pre-installed, not even a desktop environment, so you can be very granular about what gets installed and keep you system lean.

2). Most distros will not have as much in the way of corporate control/privacy concerns. A few like Ubuntu or Fedora are more closely linked with a single company, but most are more community driven and this is not a concern.

3). The advice I always give to people first trying Linux is to go into it with the mindset that you are learning a new skill, as many things are simply done differently to Windows. Most things work fine, but every once in a while, especially when setting something up for the first time, it may require additional configuration steps. Very popular distros like Mint will usually have the most community resources, and you can often find posts or guides of people who have already solved some issue you run into. I would also throw one of the Arch-based distros onto your list: Endeavour OS, which is essentially a pre-configured Arch installation. The Arch wiki is one of the most highly regarded resources in the entire linux community, and even if you are not using an Arch distro, many of the guides on it can be helpful.

4). Generally speaking, my multi-monitor usage with KDE has been seamless. No issues that I can think of. HDR support has only very recently been added, so I am not sure how well it works, but it is improving rapidly.

5). I think Plasma would be a good fit for what you are trying to do. Honestly, it is very customizable, but perfectly usable right out of the box even if you do not want to do anything to it. The layout is very familiar for a Windows user.

Okay, people have said many good things so far, so I won't add much. Simply one thing: take one problem at a time.

By this I rather mean, make your life easier, and only progressively deal with more complicated things. When it comes to distro choice, this would mean picking something with plenty of default installed packages (since you won't necessarily know what to install yourself) — this rules out my beloved openSUSE Tumbleweed as well as the popular Fedora and Debian — something that will play nice with NVidia (Desktop Environments use display managers/servers, the two most common being Wayland and X11; Wayland is better, but unfortunately will really mess up NVidia gaming, so try to stick to X11 for now — you can always switch later!), and, lastly, something with a large community (and by extension a large help forum and wiki).

I never thought I'd hear myself (see myself?) saying this (typing this!?), but Mint checks all those boxes.

I wouldn't recommend staying with Mint for long (though some people claim to enjoy it...), but as a first distro to introduce you to Linux, it really may be the easiest. Using a different DE is already difficult, don't overwhelm yourself from the get-go!

Alright, that ended up being longer than expected. I wish you the best of luck, and a lot of fun on your approaching Journey!

So I don't really have experience with the gaming aspect as I pretty much get what I want from a steamdeck. I think its likely you would want to go with one of those (a gaming setup someone else suggests) or dual boot to have your gaming system and your doing other things setup. Just in case I will mention the one I use called zorin. It is based on ubuntu with gnome and its main claim to fame is its an out of the box distro that tries to emulate windows (other systems to but the paid for version unlocks that. its default is a general windows type experience). Out of the box means it has foss office, video file viewing, audio file listening, image file viewer, browser of course, rdp client, mail client, calendar, contacts, also image,video,audio file creation and editing, optical disk copier/image creator, wine with play on linux so that you can right click a windows executable and run it and such. It does non free software things like nvidia drivers right off the bat. Its great for an install and get going right away type of thing. Its always a bit out of date because its emphasis is stable, just works, get going type of thing. I have a few complaints. Mainly it does not have the windows key, right arrow thing to half screen by default. It could be a stability thing that they don't want to mess with the compiz or whatnot. Then the other thing is I find the software gui interface it have an aweful search for getting more software so either just use apt at the command line or download the .deb installation file which things like various browsers have as a linux option for download and then its really just like adding one to windows or mac. download and run the installation.

I don’t have anything to say that everyone else hasn’t so I’ll just wish you good luck and hope you have an enjoyable experience

1. It matters as some distros have one maintainer or will offer you something ideological at great sacrifice, but you seem to already know that.

2. No, the biggest difference is package manager, community forum in case you meed troubleshooting, default DE (eases troubleshooting), and release type.

There are three big families of distros: Debian / Fedora / Arch. Any distro that is a derative of either of these three use their package manager.

3. Drop tuxedo and take a look at endeavourOS. It's arch-based and arch has the best package manager of all. Also KDE is their main DE. I use Manjaro because I prefer Xfce.

In case you do use EndeavourOS, one warning, DO NOT USE THE ARCH FORUM FOR TROUBLESHOOTING!!

(If you've heard of 'Sheldon Cooper' from the tv-series 'Big Bang theory' or 'Young Sheldon'. This forum is run by a real life version of him and you will get banned there immediately or very quickly, unlike other forums. Rule #1 of many is that any user troubleshooting admits that the issue is occuring on any OS other than Arch, including the closest deratives, will get banned.)

4. No. Don't know what HDR is.

5. Tinkering with the DE is definitely fun and you should play with it. Be careful though, because the freedom you're allowed also allows you to break things. But tinkering with the DE isn't the worst thing you could break.

Others have already answered your questions, so I'll just drop in my anecdotal experience to moving over my desktop to Linux last year. I tried a few different distros but settled with Fedora KDE edition. It works with everything exotic in my laptop out of the box, except for the gyro that doesn't work with anybody else either. The desktop feels familiar and is easy to customize. I tried to like Gnome and variants but it is really settled on The Gnome Way of doing everything. Fedora is a fresh experience from previous attempts of going full Linux desktop with Ubuntu and even Mint. The GUI for software and package management is neat and includes native packages, flatpak both the fedora builds and mainline. Some minor things are not quite there but I believe that will be the Linux experience forever and I'm okay with it. I recommend to try it.

try a bunch in live usbs and see for yourself