I think me admitting not understanding something and following advice of trusted humans is a very different thing than will full ignorance and you framing it as such is telling of the ivory tower you sit in.

Maybe what you tell me about flatpac being better and more secure is right, but trusting you, a stranger from the internet is certainly not better than trusting friends studying in the field. Is flatpack the more secure version of the aur though? The aur ist fully foss, so public scrutiny takes places. In my mind, flatpac wasn't, but maybe I'm wrong here.

As for point 5.: again: I don't argue that the way its done in Linux is bad or without reason. I just state that it is more difficult for the end user.

For btrfs: As for my understanding: the graphical installer only supports one option for encrypted file system: lvm-ext4. When you select encryption it is not possible to select btrfs anymore (or any other). As soon as you tick "encrypt system" it defaults to luks-->lvm-->ext4 and doesn't allow you to change it Maybe because it only support encrypted lvm and subvolumes won't work with btrfs (+to quote your own link: "The DebianInstaller can format and install to single-disk Btrfs volumes, but does not yet support multi-disk btrfs volumes nor subvolume "

I don't understand the part about "rsync", but im pretty sure its not what I had in mind when talking about first time user friendly options.