You are 90% of the way there.
Just keep your system up to date (update packages weekly maybe) and you will be fine. The system mostly manages itself.
I recommend installing both the current kernel and an LTS kernel. If you ever have a problem with a driver or a filesystem or something after an update, just boot into LTS and you are back up and running.
Unlike the Wine based stuff (Bottles, Winetricks), this runs actual Windows as a VM. So compatibility will be far better though performance will be worse.
Packages and package managers differ between distros. If you are changing distros, you should not try to preserve your package list. You will need to reinstall them.
However, you can often preserve your configurations and customizations by migrating the dot files in your home directory (or the entire home directory).
This is why many people put /home on its own partition. They can then wipe and reinstall the root partition while preserving /home.
You will get XFCE 4.20 at least. You can run Wayland now if you use Labwc as a compositor.
Even as a Wayland fan though, I would stay on Xorg for now if you are using XFCE.
Proxmox upgrade was flawless for me as well.
This is not the correct take.
For example, the suggestion to put /home on a partition to allow switching distros without data loss is an example of flexibility Windows does not have.
Most of the configuration that makes your desktop unique is held in your home directory, unlike Windows that spreads things across the system (such as the registry).
That said, if you do not know Linux, it is difficult to explain your options in a comment.
I am not sure what Windows automation you are referring to. If you mean upgrades between versions, Linux distros do that too. If you mean automatic migration from other operating systems, I am not aware of any Windows functionality for that.
MX is a nice distro. However, it is also true that it is just Debian with XFCE, KDE, or Fluxbox on top.
Your comment about not “being a fork of a fork” is ironic. MX Linux is a fork of AntiX which is a fork of Debian.
This is a not a criticism of MX. I love EndeavourOS and it is just Arch with a different installer and some sensible defaults. But I can also understand why some people look at MX and wonder why they don’t just install Debian with XFCE directly.
There needs to a single “App Store” where regular people can find free and paid apps that will work on all distros.
Basically, we need Steam for non-gamers.
Your mate is running a Jellyfin client on Unraid? Or the server? Unraid is a NAS that can run VMs and containers. It is not a desktop system.
If you were only running server stuff on that machine, I would recommend Proxmox.
As others have said though, basically any Linux distro can do what you are looking for.
If you are going to run it as a desktop, pick a distro that has a desktop environment (GUI) that you like and go from there.
Fun fact: Unraid is really just Slackware Linux running the Unraid application on top
Niri rocks
The appeal of Flatpak is not that I prefer it to my distro package manager.
The appeal is for the application author who finds the fragmentation in Linux a problem. It is a way for them to target “Linux” and not individual distros. It is a way for app authors to control the distribution and the support surface in a way that turning over control to package managers does not allow.
Which means the appeal for me is just that I can get apps as Flatpak that I cannot find in my distro repo.
On Arch, I hardly ever use Flatpak. On other distros, I use them more. I do use the pgAdmin Flatpak everywhere though because all the distro versions I have tried are garbage.
They are aiming for complete compatibility. They literally use the GNU test suite.