Linux Mint Debian Edition. You can use Debian testing repos for more updated packages and kernels if you want. Also, it seems like more and more applications are adopting flatpak anyway.

Now I am faced with needing to replace my SSD which gives me reason enough to install a new distro.

Replacing an SSD is pretty simple on Linux; just copy over the data, adjust the partitions, select the new drive in UEFI/BIOS. If you want to try a different distro, any time is good, but a new SSD doesn’t require a reinstall.

My advice from my distro-hopping days is to dual-boot with potential new distros (unless space is at a premium). I just made sure to share important folders like /home/. That way, if I didn’t like my new setup, I could quickly fall-back to the old.

Since you have experience on Linux, why not Arch Linux. It’s not that hard-to-master-install from the past since “archinstall” exists.

And you get a system with all your wishes of combinations that exist in the linux world. And the best well documented Wiki from Arch stays at your side.

Alternative would be fedora, easiest installer of all. And their logic of “just all firmwares, can’t fail” should help nvidia users out-of-the-box.

Highly recommend Pop_OS. It’s Ubuntu minus the bad parts, like snap. Been running it a couple years now and had few issues.

I’m using OpenSuSE Tumbleweed and can recommend that. It’s user friendly, especially with the powerful Yast tools for configuring a lot of things. I’m using KDE but it does have a good Gnome spin.

All of the tools you’re using will work without issue, and I have an Nvidia 3070 which I’ve set up without issue with the official Nvidia drivers. I game a fair bit with steam and everything works well.

If you’re not a fan of rolling release then OpenSuSE Leap is the same but point release.

OpenSuSE has good official repos and large variety of community repos, plus Flatpak if you need it. The only difficulties I’ve had are with Python which is installed in a weird way to allow multiple versions to be installed for devs - it can be fiddly installing python software dependencies into the right places, especially if they want you using pip.

Also you said you use VirtualBox - I used to use it but have switched to KVM and strongly recommend it. Guest systems - particularly Linux guests - work better in KVM. Worth exploring in your next system - in OpenSuSE it’s been a doddle to set up but should be in most systems.

I see people recommending immutable desktops - I’d be cautious about switching your desktop to that if you don’t have experience of that kind of system. They have strengths but definite drawbacks too. I’d try another distro not too disimilar to Ubuntu before exploring the world of immutable distros.

Maybe try an immutable system in a Virutal machine. I’ve played a bit with them and they’ve not been for me - too locked down and if you like to tinker or try niche things you’ll find yourself fighting the OS. Also Flatpak is convenient but it’s not the ideal or most secure way to be running all your software, and lots of software isn’t available as Flatpak.

And for Nix, it is very good but can be used on many distros. You can get another traditional distro and try it out - if you like it by all means switch to NixOS but you don’t have to use NixOS to use Nix. Again it seems too big of a leap to go all in to that on your main desktop. I’d make a smaller change unless you’re open to reinstalling your main desktop a few times trialling bigger shifts.

I am not a big fan of snap, and I would prefer a more logical and unified package management system

That’s exactly where Snap is going!

Seriously tho, Ubuntu is fine. The LTS versions are always extremely solid. Your objections sound more theoretical than practical and you also seem to be running quite advanced hardware and software. The least risky strategy would be stay where you are.

Standard fedora

Always advocating for that but Aeon Desktop (immutable OpenSUSE) has been great for me: rock solid base system, latest Gnome desktop, all the apps in Flatpak. Distrobox for all the terminal applications needs works better for me than the toolbox on systems like Silverblue. Give it a try!

For good out-of-the-box nvidia support, I recommend Bazzite.

Stay with Ubuntu LTS or go Debian.

pop is a pretty similar distro that should be compatible with what you want to do, but i’m not sure how much it hits for a more unified package management system. it’s really hard to beat the AUR and a AUR helper like paru for that.

I’m similar in apps, and I get along nicely with Fedora. Had to muck about a bit to get Auto1111 working, but otherwise no issues. I use a fair number of flatpaks where Ubuntu offers snaps. I use VMware instead of virtual box, and that was a pain to install. Nvidia plays nice if you set up rpmfusion repos.

Nix is the best packaging system. One of the best kept secrets is you can download old packages from github and it will install old deps into a different folder. Very useful for just downloading the exact wine version you want or keeping a broken package at the version it still worked on. I’d use bottles, but the wine versions it provided were not the latest!

So NixOS, being based on Nix is the best distro