You didn’t read the magazine article carefully. As the magazine says, Guest Additions need to be installed inside the VM, not on your host OS.
The scripts are to be run in the guest OS, and are included in the guest addition CD. Insert this CD to your guest OS by clicking Devices → Insert Guest Additions CD image… in Virtual Box.
Also, the article’s method is outdated, just like the magazine’s comment says, install this on your guest OS
What you really need for your host OS is Oracle’s VirtualBox Extension Pack, which is proprietary (subject to VirtualBox_PUEL – Oracle VM VirtualBox), and must be downloaded from VirtualBox’s website (not rpmfusion): Downloads – Oracle VM VirtualBox. This is not needed for basic function of VirtualBox, but as you said you want to connect hard disk through USB,
I can’t attach any external drive to my virtual machine (I have three connected, two HDDs and a thumbdrive), none are detected in the machine settings:
then it’s necessary because this Extension Pack provides USB 2.0 and USB 3.0 ability.
Is it mandatory to install Extension Pack and Guest Additions for the machine?
Yes, it is, for USB 2.0/USB 3.0 ability.
My suggestion: qemu/kvm. It is a trully FOSS alternative, and can be easily controlled by virtmanager (sudo dnf install virt-manager). Also, you don’t have to insert out-of-tree kernel modules from virtualbox, it’s in the kernel main tree. One drawback is that virtmanager does not provide easy guest integration like sharing files between guest and host (well, at least for non-linux guest; you can share filesystem for linux guest), which is pretty inconvenient. But as for USB qemu/kvm does it pretty well, no extra packages needed.
I guess it’s because fedora has stricter licensing issues and packaging standards than other distributions (debian, arch, etc.). Fedora’s repository cannot contain non-free or patent-encumbered software, and even reject free software not conforming to Fedora Packaging Guideline (FYI, programs written in Go or Rust is known to be hard to package). Rpmfusion will accept more packages, but these packages have to be at least legally redistributable
According to https://rpmfusion.org/FAQ#What_packages_are_available_from_RPM_Fusion.3F
Does RPM Fusion distribute illegal software?
No. RPM Fusion only distributes packages which can be legally re-distributed.