1. Ubuntu studio is already stupid easy to install and has recording and gaming support out of the box?
2. You're right that a lot of people around here don't like Ubuntu. But it IS stable. And I'm not sure as a Linux noob you're even going to notice the things that they don't like. You could always try out multiple distros before choosing which one you'll stick with. I'm not aware of any other distros like Ubuntu Studio. I use it on one of my laptops because it has great midi keyboard software pre installed for free. It's just about the only way to get similar software for free without compiling it from source code yourself.
3. If you have no other computer, please make a backup Linux install USB and put it in a safe place. You will have absolutely no way to save your system if it fails. Even Windows fails sometimes. Maybe look into Linux system rescue specific distros.
4. Ubuntu is already Debian based (in case you didn't know).

Edit: by gaming support out of the box I mean: just install one of the following apps through the Discover app: Steam, Lutris (supports multiple game launchers including Steam and EA), and/or Heroic Games (for GOG and Epic). There's even a few more launchers like Bottles, but I never had much luck with it. There's several options for Minecraft launchers. And, there's even many open source games you can install directly through Discover. I recommend Super Tux Kart. It's solid.

This advice is true for pretty much any distro, although the name of the app manager changes.

I don't know of an "out-of-the-box" distro for multimedia outside of Ubuntu Studio, but I do know of a utility that will turn any distro into a low-latency, pro audio setup: rtcqs - it runs 10-12 tests on your system and tells you how to set it up for realtime audio, if it isn't already - this is very much NOT what you asked for, but if you get your system going but it's not performing like you expect, this could be the thing that fixes all your issues.

Linux Mint is usually touted as being the most beginner-friendly Linux. Its UI is very Windows-like, it has a large enough userbase to have enough programmers to be able to have good configuration tools.

And of course, because it's anyways based on Ubuntu, 95 % the support documentation for Ubuntu works for it as well.
Ubuntu-based of course means, it's also Debian-based.

I personally find using an immutable distro fairly annoying (as there's a lot of packages that you can't easily install), and would recommend either the KDE or Gnome versions of Fedora, depending on which you like best. It could be a little easier to break but I think you're very unlikely to run into any problems with it that wouldn't happen on an immutable distro. Unless you intentionally mess with system packages or something

I recently switched to Ubuntu Cinnamon. I like it a lot, but I've had some headaches making some things work. It's worth it me, as I will never return to Windows. I relied heavily on chatgpt to get me through tweaking it. Any errors I would receive in the bash terminal, I would paste into chatgpt and it would give me step by step instructions on what to do. I would have thrown the laptop in a pond without that, though. The technical barrier to entry isn't too high, so long as you exercise a little patience.

I moved to Bazzite and really liked it. You lose a little bit of control (encouraged to do things the bazzite way because it’s based off fedora atomic) but the ease of use more than makes up for it.

Unraid its simple when you have some mismatching drives

I use OpenMediaVault. Took a little bit of effort to install Docker, but that lets me toss up most self-hosted services on a whim.

Your os disks should be raid 1. I'd recommend a pair of onboard nvme or cheap ssds for OS. That's the part you don't want to be fighting with if something does go wrong.

It's trivial to replace a drive on zfs if one fails.

Hardware and software are both really reliable these days. If you're running something like proxmox then you also get easy snapshots and rollbacks.

Yes, but perfectly reliable hardware is impossible and every small gain in reliability drastically increases the price. Luckily, most hardware can be "fixed" by replacing the malfunctioning part. The only part that is not easy to replace is hard drives. For data disks, I have guides giving me step by step institutions on how to rebuild off of replicas. With the OS disk, I am depending on hopes and taking notes while installing.

Broken software is tricker to replace. I can uninstall and reinstall it, but I have to be careful to avoid catastrophic data loss. Also, broken software generally means a bad release, so I have to revert and periodically upgrade/revert to check if the issue has been resolved. And running old versions of one part of the system can cause incompatibility in other parts.

Debian Stable. Debian is what you choose when you don't want to fuck with it.

Using unreliable hardware seems at odds with your "just want it to work" requirement.

The reason that I was favoring Greyhole over ZFS is that I want to assemble a large, redundant storage volume out of a bunch of mismatched old disks and swap them out as they fill up or fail. I know it is very possible to do it with ZFS, but it seemed to not be the general use case and complicated.

+1 for Debian. It just works like advertised and with no fuss.

I run Debian on my NAS, it take some time to configure everything like you want it from the command line, but once it's done you can pretty much forget about it. You could look into OpenMediaVault and CasaOS if you want to have a WebUI to do the configuration. My personal experience with OMV was not so great but it was a long while back and I was trying to run it on an ARM single-board computer, so it might actually be good on a more standard setup. It's also Debian under the hood.

If you want the machine to just work and not require or encourage you to fool around with it all the time, debian is the answer. Other than installing security updates, you don't have to think about it.

I run my home server with Debian and docker.

I use Open media vault. It's more or less a turn key file server.

Maybe truenas.

Personally I just run proxmox at home with zfs for my array, then everything lives in a few vms / containers.

Thank you for the warning.

that's maybe not that bad then. but do know that websites can run HTTP requests against localhost and lan addresses, any ports, maybe WebRTC connections too. ublock has a built in list against that.

The last step fails, and I assume that’s why I’m now in trouble.

$ sudo apt modernize-sources E: Invalid operation modernize-sources

Not sure about the error but I kind of doubt modernize-sources would make/break your upgrade. I did a clean full install of Debian 13 and the sources file wasn't even modernized on that, it's still the old version. Would be very surprised if somehow sources is following a different requirement for a Debian 13 upgrade.

From the error maybe your version of apt doesn't support the "modernize-sources" option.. but that itself isn't relevant to your Debian upgrade.

There shouldn't be any updates available after doing a full upgrade. Maybe you forgot one of the apt full-upgrade steps. That should have upgraded apt to give you new options. So just do that.

I'd also use the official documentation. https://www.debian.org/releases/stable/release-notes/upgrading.en.html

A client uses teams and we use zoom. I use both in the browser.

You can also try Bottles for some exe games instead of Lutris.