It is not like ‘very limited’. But generally they are focused around modern Intel CPU, and can have issues on new AMD CPU. And it won’t work on very old CPUs without proper virtualization features.
https://www.qubes-os.org/hcl/ can hint on what Qubes will work better.
Also see the system requirements: https://www.qubes-os.org/doc/system-requirements/
Probably, yes. Qubes AppVMs don’t run the whole DE inside it. Also, Qubes uses automatic memory balancing for VMs, so users doesn’t need to care about it much.
Sorting order preferences.
Threadiverse? I didn’t hear this name, I think it can be confused with Meta’s threads.net. But I don’t like Lemmy, and don’t want the network to be named after it. For example we don’t call Fediverse as Mastodonverse.
As for Mbin, UI looks good, a feature showing similar threads is useful. But it is quite new yet, many important options are missed in the preferences yet.
Oh, it is annoying part of GNU/Linux that there is no way to override /usr/share/* resources system-wide. It is possible to do for each user by placing files into ~/.local/share but not for the system.
As I have been using Silverblue for enough time, I would say that splitting between the base OS and the apps is an important thing but atomicity/immutability of the base system is not so much.
For example: I also use QubesOS and it gives quite immutable-like experience while the base distro is a regular non-atomic Fedora.
By using flatpaks (or snaps) or tools like distrobox on a regular distro you will get a similar experience.
The main think is to cut dependencies between apps and the os and to be able to update them independently.
And then, when you have the apps separated, there are just not many reasons against choosing an immutable distro for the base system because it gives you additional bonus things as safe updates and rollbacks. But you can use a non-immutable distro as well if you want a specific or a niche distro (for example Chimera Linux or Alpine).
But the majority of distros provides it as a default choice. FF for Linux is like Edge for Windows.
Right now statcounter shows:
Firefox: 2.74% Linux: 1.61%
Shattered Pixel Dungeon is a perfect game for girls. And yes, you can care for pets there.